Southwest Koi and Pond Association





Norm Meck

copyright 1996,1999,2000

Revised 10/30/01 - page 21

Table of Contents

Preface Page 2 Test Kits Page 2

Ammonia Page 4 Nitrite Page 7

Nitrate Page 9 PH Page 10

Alkalinity Page 11 Temperature Page 14

Dissolved Oxygen Page 15 O2 during Transport Page 19

Salinity Page 21 Clorine Page 22

Homemade Chlorine Neutralize Chloramine Page 23

Water Change Outs Page 24 Green Water Page 26

Pollutants Page 28 Toxic Plants Page 29

Final Thoughts Page 30 Conversion Factors Page 31.2

Pond Water Chemistry

Norm Meck, Koi Club of San Diego

copyright 1996,1999,2000

This is a composite of a series of articles dealing with the chemical makeup of pond water. How to

measure what is in it, what is good, what is bad, and what to do about it. Before starting, I would like to

discuss the name applied to what has typically been called the "bio-filter." A filter is defined as a porous

device through which water (or gas) is passed to separate out matter in suspension. The biologic activity

within the pond "filter" does not trap the matter in suspension but acts on dissolved components that

could not be separated regardless of how fine the filter pores. Although this device may perform a dual

role as a mechanical filter, to emphasize the processes of interest, you will see that I will often refer to it

as the biologic converter or bio-converter, not as a filter.

By introducing fish into your pond, you have assumed the responsibility for the care of these creatures.

This includes not only feeding them but also providing them with a healthy environment in which they

can live and thrive. Partial determination of the quality of this liquid environment can be made through

chemical measurements. It seems somewhat ludicrous that someone would spend hundreds or thousands

of dollars to build a pond and then add hundreds or thousands of dollars of beautiful Koi but would not

buy and learn how to use a ten dollar nitrite test kit. This doesn't mean that one must test the water every

few minutes or even every few days. An established pond with the fish appearing healthy should be

checked every month or so. It is only when something out of the ordinary is observed and possibly

during seasonal changes when an additional test or two might be needed. A simple test at the right time

may prevent a small problem from becoming a catastrophe. When starting up a new pond or bio-converter

system, daily tests may be required until the converter comes on line, then weekly for a couple

of months until the system has stabilized.

Just as when medicinally treating your pond, it is imperative to know the total amount of water in your

pond and converter/filter system as accurately as possible. Over treatment or under treatment with

chemicals can be equally disastrous. Don't guess on quantities, measure them!

Do not confuse the terms water quality and water clarity. Crystal clear water can contain compounds

that are deadly to your fish. Green water, sometimes called an algae bloom and caused by excessive

phyto plankton growth, can actually be beneficial to the fish although not very beneficial to the pond

keeper who can't see them. Water clarity can give some indications as to mechanical filtration


A pond with a biologic converter and filled with Koi is a rather complex, somewhat self-contained

ecological system. Each component of this system requires the other components to survive and prosper.

The basic portion of the cycle is shown below. Fish waste and other organic waste is converted by

bacteria and fungi to ammonia compounds. These compounds can be injurious to the fish, but a healthy

biologic converter populated with families of bacteria consume these ammonia compounds and convert

them to nitrite. Unfortunately, nitrite is just as toxic to the fish as the ammonia. Again, the biologic

converter comes into play with another colony of bacteria that convert the nitrite to nitrate. The nitrate is.3

basically inert to the fish but usable by plants and algae within the pond. As the plants and algae grow

and the Koi eat them, the cycle starts all over again. The bacterial colonies that do this conversion are

called aerobic since they require oxygen to convert their "food" to energy just like the fish.

Pond Nitrification Cycle

Test Kits in Estimated Order of Importance


pH Ammonia

Nitrite Thermometer

Nice To Have

Alkalinity Salinity

Nitrate Dissolved Oxygen

Probably Not Necessary

Chlorine Hardness.4


Ammonia, NH3, measured in parts per million (ppm), is the first measurement to determine the "health"

of the biologic converter. Ammonia should not be detectable in a pond with a "healthy" bio-converter.

The ideal and normal measurement of ammonia is zero. When ammonia is dissolved in water, it is

partially ionized depending upon the pH and temperature. The ionized ammonia is called ammonium

and is not particularly toxic to the fish. As the pH increases and the temperature drops, the ionization

and ammonium decreases which increases the toxicity. As a general guideline for a water temperature of

70 O F, most Koi would be expected to tolerate an ammonia level of 1 ppm for a day or so if the pH was

7.0, or even as high as 10.0 if the pH was 6.0. At a pH of 8.0, just 0.1 ppm can be dangerous.

Two types of ammonia test kits are commonly available. The first is based on the Nessler reagent. This

kit normally uses drops in a water sample with an associated color chart. The second is a salicylate

reagent test that may use drops, powders, or pills and is usually a two step process again followed by a

color chart. The Nessler kit provides a faster test but is not compatible with any ammonia treatment

chemicals that may be in the water (more about those later). One way to determine which type of test kit

you have is that the Nessler kit color chart normally ranges from clear, meaning no ammonia, to

yellow/yellowish-orange as ammonia levels increase. The salicylate based test kit ranges from a light

yellow, meaning no ammonia, to green/bluish-green as ammonia levels increase. Both types read the

total of ammonia and ammonium, so without knowing the temperature and pH, the toxicity cannot be

determined. Suffice it to say that the only good ammonia reading is zero. But note that any pond.5

containing fish will have some residual ammonia. The bio-converter does not remove all of it each pass

and the fish continuously add it to the pond. The residual level will be determined by the fish load, the

effectiveness of the bio-converter, and how often the water is passed through it. This residual level

should not be detectable on the average test kit. The recommended test kit should be able to detect 0-1

ppm of ammonia. An ammonia test kit is considered to be a requirement for all pond keepers.


Ammonia tends to block oxygen transfer from the gills to the blood and can cause both immediate and

long term gill damage. The mucous producing membranes can be destroyed, reducing both the external

slime coat and damaging the internal intestinal surfaces. Fish suffering from ammonia poisoning usually

appear sluggish, often at the surface as if gasping for air.


Ammonia is a gas primarily released from the fish gills as a metabolic waste from protein breakdown,

with some lesser secondary sources such as bacterial action on solid wastes and urea.


Ammonia is removed by bacterial action in the bio-converter and a small amount is directly assimilated

by the algae and other plants in the pond. The bacteria consume the ammonia and produce nitrite as a

waste product. A significant portion of this bacterial action can occur on the walls of the pond as well as

in the pipes and bio-converter. Ammonia readings may increase with a sudden increase in bio-converter

load until the bacterial colony grows to accept the added material. This can happen following the

addition of a large number of new fish to a pond or during the spring as the water temperature increases.

Fish activity can often increase faster following a temperature increase than the bacterial action does. A

bio-converter that becomes partially obstructed with waste and/or develops channels through the media

may operate at reduced effectiveness that can also cause the ammonia levels to increase.


Chemical treatments to counteract ammonia toxicity are available commercially under various trade

names. These treatments, most of which are based on formaldehyde, chemically change the form of the

ammonia into compounds that are not harmful to the fish. They do not actually remove it from the pond.

The bio-converter bacteria still does the actual removal. Although most of these products use a dosage

of 50 ml per 100 gallons to chemically bind up to 1 ppm of ammonia, be sure to check the

manufacturer's directions before use as those containing formaldehyde can result in overdose conditions.

Note that the Nessler type test kits may show false readings when any of these chemical treatments are

in the water. If a pond has a healthy bio-converter, there is normally not only no need to treat with

ammonia binding chemical agents, it is better not to use them at all.

When ammonia is detected (assuming a pH of about 7.5):

Increase aeration to maximum. Add supplemental air if possible.

2. Stop feeding the fish if detected in an established pond, reduce amount fed by half if starting

up a new bio-converter/pond.


3. Check an established pond bio-converter for probable clean out requirement

4. For an ammonia level of 0.1 ppm, conduct a 10% water change out. For a level of 1.0 ppm,

conduct a 25% change out.

5. Chemically treat for twice the amount of ammonia measured.

6. Consider transferring fish if the ammonia level reaches 2.5 ppm.

7. If starting up a new bio-converter/pond, discontinue use of any UV Sterilizers, Ozone

Generators, and Foam Fractionators (Protein Skimmers).

8. Retest in 12 to 24 hours.

9. Under Emergency conditions only, consider chemically lowering the pH one-half unit (but not

below 6.5).

CAUTION: If the tap water has a higher pH than that of the pond or if the tap water

contains Chloramine, adding the replacement water may make the situation worse..7


Nitrite, NO2-N, measured in parts per million (ppm), is the second chemical measurement made to

determine the "health" of the biologic converter. Nitrite should not be detectable in a pond with a

properly functioning bio-converter. Thus the ideal and normal measurement of nitrite is zero. A low

nitrite reading combined with a significant ammonia reading indicates the ammonia-nitrite biologic

converter action is not established, while a low ammonia reading with a detectable nitrite reading

indicates that the nitrite-nitrate bacterial conversion activity is not yet working. Test kits are available in

pill, powder, or droplet forms with color charts. Recommended test kit range 0 - 4 ppm. A nitrite test kit

is considered to be a requirement for all pond keepers.


Nitrite is produced by autotrophic bacteria combining oxygen and ammonia in the bio-converter and to a

lesser degree on the walls of the pond. Just as with ammonia, nitrite readings may increase with a

sudden increase in bio-converter load until the bacterial colony grows to accept the added material. This

can happen following the addition of a large number of new fish to a pond or during the spring as the

water temperature increases. Fish activity can often increase faster following a temperature increase than

the bacterial action does. A bio-converter that becomes partially obstructed with waste and/or develops

channels through the media may operate at reduced effectiveness that can also cause the nitrite levels to



Nitrite has been termed the invisible killer. The pond water may look great, but nitrite cannot be seen. It

can be deadly, particularly to the smaller fish, in concentrations as low as 0.25 ppm. Nitrite damages the

nervous system, liver, spleen, and kidneys of the fish. Even lower concentrations over extended periods

can cause long term damage. Short term, high intensity, "spikes" which often occur during a bio-converter

startup or restart may go undetected yet cause problems to develop within the fish months

later. A common indication of a fish that has endured a severe nitrite spike in the past is that the gill

covers may be slightly rolled outward at the edges. They do not close flat against fish's body.


About the only control of nitrite is through the maintenance of a "healthy" bio-converter. Within the

media, the bacteria combine oxygen with the nitrite to convert it to the relatively benign nitrate. These

bacteria receive considerably less energy from this conversion process than do the bacteria carrying out

the ammonia to nitrite conversion process. For this reason, they are not as hardy and tend to be the last

to come and the first to go when a problem occurs within the bio-converter. Water change outs can

reduce the levels temporarily by the same amount as the percentage of water changed. The addition of

salt helps reduce the toxic effects significantly but should only be used as a interim measure, not as an

ongoing treatment.

Whenever 0.25 ppm of nitrite or more is detected in a pond:

1. Increase aeration to maximum. For a nitrite level of 1 ppm or greater, add

supplemental air, if possible..8

2. Stop feeding the fish if detected in an established pond, reduce amount being fed by

half if starting up a new bio-converter/pond.

3. Discontinue use of any UV Sterilizers, Ozone Generators, and Foam Fractionators

(Protein Skimmers).

4. For a nitrite level less than 1 ppm, conduct a 10% water change out and add 1 pound of

salt per hundred gallons of changed water.

5. For a level between 1 and 2 ppm, conduct a 25% water change out and add 2 pounds of

salt per hundred gallons of changed water.

6.For a level greater than 2 ppm, conduct a 50% water change out and add 3 pounds of

salt per hundred gallons of changed water.

7. Retest and repeat above in 24 hours.

8. For nitrite levels of 4.0 or greater, consider transferring fish.

CAUTION: Again, if the added water contains Chloramine, the added

ammonia after conversion to nitrite may make the situation worse..9


Nitrate, NO3-N, measured in ppm, is the third and last measurement used to determine the "health" of

the bio-converter. Nitrate is produced by one of the autotrophic bacterial colonies by combining oxygen

and nitrite. This occurs both in the bio-converter and to a lesser degree on the walls of the pond. A zero

nitrate reading, combined with a non-zero nitrite reading, indicates the nitrite-nitrate bacterial converter

action is not established. Test kits are available with dual droplet or pill form with color charts. The

recommended test kit range 0 - 200 ppm. A nitrate test kit is considered nice to have but not required for

the average pond. In an established pond with part of the routine maintenance including 5% to 10%

water change outs every week or two, nitrate levels will normally stabilize in the 50-100 ppm range.

Concentrations from zero to 200 ppm are acceptable but should normally be below 100.

Where ammonia and nitrite were toxic to the fish, nitrate is essentially harmless. There have been

reports that high nitrate levels may weaken the colors in Koi, but there have also been reports that high

nitrate levels can enhance the colors. Similarly, I have read reports, fortunately not in the same article,

that high nitrate levels will both stimulate and suppress spawning activity. If the nitrate concentration

gets too high, the nitrite-nitrate converting bacteria may not be able to do their job effectively resulting

in a raised nitrite level. Nitrate is the end result of the nitrification cycle and is very important to plants

in their life cycle. This is why the plants in your garden can flourish from being watered with the waste

water from your pond (assuming you haven't added too much salt).

Note the large difference in the ranges of the test kits being used to measure nitrate (200 ppm) as

opposed to those for ammonia and nitrite (1-4 ppm). Assuming our the bio-converter was converting the

equivalent of 1 ppm of ammonia to the equivalent of 1 ppm of nitrite to the equivalent of 1 ppm of

nitrate per day, it would take 100 days or over three months, (longer with any water change outs), for the

nitrate levels to build up to the 100 ppm level. The nitrate concentration is controlled naturally through

routine water change outs and to a lesser degree through plant/algae consumption..10


For the record, pH is technically defined as the negative base 10 logarithm of the effective hydrogen ion

concentration in gram equivalents per liter (whatever that means, and why is it spelled so pHunny?) We

are going to skip many of the technical details since it is not really necessary that a pond keeper knows

exactly what pH is. What is important is to know how to make pH measurements, to routinely make the

measurements, and how to interpret their results. The discussion below is not intended for chemistry

majors nor for anyone who desires a technically accurate description of our subjects. It is provided for

the average pond owner to visualize what is going on in his or her pond.

Various substances exhibit similar characteristics in how they react with other substances. A broad range

of these characteristics has been divided into the two categories, acid and base, where the pH

measurement is related to a ratio of the base components to the acid components. (We aren't going into

what these components actually are.) If a substance has one acid component for each base component, it

is said to be neutral and has a pH value of 7. Greater than 7 is less acid, more base, and less than 7 is

more acid and less base. Each unit is 10 times the previous, i.e., a pH of 9 is 10 times more base than 8,

a pH of 5 is 10 times more acid than 6. Some examples of more acid like things are vinegar, orange

juice, and the liquid in your car battery that makes holes in your clothes. Bases include lye, antacids for

your stomach, and brushing your teeth with baking soda. When acid like substances are mixed with base

like substances, they react with each other producing some byproducts and leaving the resulting solution

with a pH somewhere between the two original values. The further apart the pH of the two substances,

the more energy is released in the reaction. Put a teaspoon of baking soda in a half glass of vinegar and

see what happens.

We are familiar enough with the extremes of acids and bases to know it is not a good idea to place a bare

hand in either battery acid or caustic lye, and we can assume that neither would be a good place to put

our fish. A pH measurement will help us determine if our water is a proper place to put the fish. For our

Koi ponds, the pH should normally be between 7.0 and 8.5, but it is probably acceptable to be anywhere

between 6.0 and 9.0. Although most of the fish could tolerate a pH as low as 5.0, bio-converter bacteria

are subject to damage. Long term conditions above 9.0 can cause kidney damage to the Koi.

Test kits are available that use drops, pills, or powders with a color chart to show various ranges of pH.

A wide range pH test kit (Range 5.0 - 10.0) is considered as a requirement for all ponds. If higher

accuracy is desired, one or more limited range test kits are nice to have for the ranges most often

encountered. Battery operated, digital electronic pH meters are available that measure from 1-14 in 0.1

increments. Most of the inexpensive versions of these ($100 or less) provide readings that are both

temperature and battery condition dependent. All require periodic calibration and the less expensive

ones usually require calibration prior to each use. Since doing this calibration and maintenance of the

meters with probe cleaning and storage solutions is more involved than making a chemical reading of

the pH, an electronic pH meter is not considered appropriate for most pond keepers. Those who have

difficulty distinguishing the small color differences of the chemical test color charts find them



Just knowing the pH doesn't give us the complete picture. A pH test of distilled water can show almost

any value since just a tiny amount of residual impurities, either acid or base, can have a major effect on

the ratio of the two.

For example: assume we have the equivalent of 1 acid component and 1 base component in our water

(equal amounts means the pH is a neutral 7). Adding 100 more base components will cause a change of

over 100 in the ratio (101 divided by 1) and cause the pH to go to just over 9. Now let's start with 1000

acid components and 1000 base components in our water; again equal amounts so the pH is still 7. If we

now add the same 100 base components, the ratio changes only slightly (1100 divided by 1000) and the

pH goes up just a little bit (to about 7.04). The Alkalinity (often called the total alkalinity) of our water

is related to the actual number of base components and can be thought of as the "intensity" of the pH.

(There is also a similar measurement called acidity related to the number of acid components but since

we are normally concerned with slightly base water, it is easier to measure the larger number of base

components than the smaller number of acid components.)

If the alkalinity is low, it indicates that even a small amount of acid can cause a large change in our pH.

Consider the pond owner whose pH was 8.0. He was told that 7.0 was better so he puts in chemicals to

lower it. The next day, it is back to 8.0 so he adds more chemicals. The following day it tests at 7.5. He

feels good because it is finally starting to come down and dumps in some more stuff. All of a sudden he

finds that the pH is 5.0. His bio-converter bacteria were destroyed and his fish are dying. Each treatment

kept reducing the alkalinity until it was so low that the final addition caused a major pH transition.

Alkalinity is related to the amount of dissolved calcium, magnesium, and other compounds in the water

and as such, alkalinity tends to be higher in "harder" water. Lime leaching out of concrete ponds is a

primary source of alkalinity but it is also slowly increased by evaporation which concentrates the source

compounds. Alkalinity is naturally decreased over time through bacterial action which produces acidic

compounds that combine with and reduce the alkalinity components.

Alkalinity is most often measured in ppm (referred to as calcium carbonate equivalents). A measurement

is normally made by pretreating the water sample with a pill, powder, or droplet solution which results

in the sample turning blue. The alkalinity is then determined by measuring (from a calibrated pipette or

by counting drops) the amount of a second acidic reagent required to change the color to pink. A

recommended test kit should measure a range of 0 - 200 ppm. An Alkalinity test kit is recommended but

not considered to be a requirement for the average pond keeper. In an established pond, the ideal

Alkalinity measurement should be around 100 ppm. Readings from 50 to 200 are acceptable.


Much more important than either the actual pH and alkalinity measurements, assuming they are both in

the acceptable ranges, are CHANGES to them. A typical established pond will normally settle down

into an equilibrium state with a pH of about one half unit above or below the pH of the tap water used

for replenishment. Over time (months), all of the inhabitants (bacteria, plants, and the fish) become

acclimated to their environmental conditions. Stress occurs in all of them if they must adjust to any.12

changes. Rapid changes in pH can cause extreme stress to the fish similar to shock in humans. A sudden

change of a half or more pH unit in an established pond is an indication that something happened and

the cause should be determined. Slow, longer term, changes provide other indications. Increasing pH

and/or alkalinity trends in a pond are normally caused by lime leaching out of concrete and to a lesser

degree by concentration due to evaporation. Decreasing pH and alkalinity tendencies are primarily due

to bacterial action that release acidic compounds. Concrete ponds usually stabilize at a slightly higher

pH value than ponds with liners.

High alkalinity is normally prevented by routine water change outs (assuming the tap water has a

lower alkalinity than the pond water). Increasing pH trends can be minimized by an initial pretreatment

or curing of a new concrete pond. Fill the pond with water (no fish), add Muriatic acid (swimming pool

acid) as necessary to adjust the pH to about 5. Circulate continuously and test daily, adding additional

Muriatic acid to maintain the pH level until no additional acid is needed. This normally takes 2-3 days.

After draining, the pretreatment cure is complete and the pond is ready to be filled for use (now you can

put in a few test fish). A properly treated concrete pond will usually reach an equilibrium state where the

production of compounds which reduce the alkalinity is matched by the components being leached out

of the concrete.

Ponds with vinyl liners or of fibre glass construction tend to show a decrease in alkalinity over time and

may need supplements to maintain an acceptable level. Raise alkalinity by adding Calcium Carbonate,

concrete blocks, oyster shells, limestone, or even egg shells. To raise the alkalinity by 40 ppm, add 1/2

oz of Calcium Carbonate (precipitate powder) per 100 gallons of water. A bag of oyster shells or even a

concrete block or two (not cinder block) submerged in the pond or filter area may be all that is needed.

Keep a close eye on the pH while adjusting Alkalinity levels. An alkalinity stabilization Apill@ can be

made from plaster of paris. Just mix water with the plaster of paris, let it harden, and put it in an area

that receives good water flow across the surface. A one pound plaster of paris Apill@ for each 500

gallons should suffice. Periodic replacement is necessary as they dissolve.

Established ponds will normally maintain their equilibrium pH value if sludge and decaying organic

material is routinely removed from the pond, mechanical filter, and biological converter. Scheduled

water change outs (10% per week for a small pond, less for larger ponds) are also helpful. Monitoring

the pH by recording weekly readings (before the water change outs) can provide an excellent indication

of any developing problems. pH values do change somewhat during each 24 hours, depending upon the

temperature, quantity of plants (algae and others), and the size of the pond, so try to take the

measurements at about the same time of day. Alkalinity measurements can provide a warning that a pH

problem may be imminent.

If the pH gets out of control on the high side, conduct daily water change outs to bring it back into

range. Recheck after each water change out and again in 24 hours. Don=t forget to check the pH of the

water being added, it may be part of the problem. At a pH of 9, do daily 10% to 25% water change outs.

For a pH of 10, do 25% to 50% water change outs. At pH extremes over 10, remove any remaining fish.

Only under EMERGENCY conditions should chemical means be used to lower the pH in a pond. Any

attempt to lower the pH chemically can be particularly hazardous to you, the biologic converter, and the

fish (not necessarily in that order)..13

A low pH problem, below 7, is normally only observed in a liner based or an older concrete based pond.

It is usually the result of a ApH crash@. This is when the total alkalinity has been consumed by the

biologic activity in the converter and the pH suddenly drops. This has been observed to go as low as 4.5.

Again, start water changeouts and increase aeration. Sodium bicarbonate (plain old pure baking soda,

Arm & Hammer or generic store brand) will raise the pH and also increase the total alkalinity.

CAUTION: Be sure to check and treat for any ammonia presence BEFORE attempting

to raise pH through either chemical or water change out means.

Repeating for emphasis, the value of the pH measurement, within the acceptable limits, is of little

importance. A change, whether sudden or a slow trend, to the pH of an established pond, indicates

action may be required and is why periodic pH measurements are important. Further, if your pH is

reasonably stable and is anywhere between 7.0 and 8.5, not only is there no need to attempt to adjust it.

You probably will do more harm than good by trying to change it..14


Whether you measure your pond's temperature in degrees Centigrade or degrees Fahrenheit or both, a

thermometer is considered a requirement for all ponds. A floating pool or spa thermometer is good. It is

recommended that it be floated in the filter/converter system or tied to an easy access point at the edge

of the pond. At a slightly higher cost, the electronic indoor/outdoor thermometers on the market (i.e.

Radio Shack) provide a continuous digital readout. Just drop the end of the waterproof outdoor probe

into the water. (Note: Small floating glass aquarium thermometers have been swallowed by Koi.)

Temperature Ideal Range 65 O F-75 O F (20 O C-25 O C)

Acceptable 35 O F-85 O F (2 O C-30 O C)

The temperature of the pond normally follows that of its surroundings although with a delay related to

the size of the pond. Direct exposure of the pond to open sky can cause larger swings in temperature.

Direct sunlight during the day can cause the temperature to rise higher, and heat loss on clear nights can

cause the temperature to drop lower than shaded ponds. A clear night sky can absorb a large amount of

heat from a small pond and actually drive the pond temperature below air temperature.

Events generally happen faster at higher temperatures and in smaller ponds. Over normal temperature

ranges, biologic activity doubles for each 10 O rise in temperature. The toxicity of ammonia increases as

the temperature rises and the amount of dissolved oxygen that the water can hold decreases. Although

Koi have been known to survive for limited periods at 100 O F and even higher, the mortality rate of fish

conditioned to 75 O F water increases rapidly above 85 O F. Above 80 O F, supplemental air may be

required. Below 55 O F (12 O C), Koi stop producing antibodies and at about 45 O F (7 O C) enter a state

similar to hibernation. Bio-converter bacteria activity ceases at about 40 O F (5 O C).

Feeding fish versus Temperature:

Less than 50 O F Do Not Feed

50 O F-60 O F 2-4 times weekly

60 O F-85 O F 2-4 times daily

Above 85 O F Do Not Feed

In all cases, try to feed only what the fish will normally consume in about 10 minutes.

Remove any uneaten food within an hour.

Fish do not like changes in their environment of any kind, including temperature. Any changes add

stress to the fish and the larger and faster the changes, the greater the stress. This is considered by many

to be the primary reason that fish do better in larger ponds. Another time that the Koi are subjected to

stress from temperature changes is when they are being transferred to a pond from another location. My

recommendation is that if the fish have been bagged for more than four hours, it is better to release them

immediately than to subject the fish to the "bad" water in the bag for an additional half-hour. Thirty

minutes of floating will prevent a sudden shock if the temperature difference is large, but it will not.15

acclimatize the fish to the new temperature. Actual temperature acclimation of a fish takes several days,

similar to us dealing with jet lag. It is not only the temperature the fish need to be accustomed to but also

the pH, hardness, alkalinity, "the taste", etc. of it's new surroundings.

Other than providing some shade (summer and winter), little can be done or normally needs to be done

to control an outdoor pond's temperature. A waterfall in dry climates can provide significant "swamp

cooler" action and a large waterfall can provide considerable cooling (at a sacrifice of additional water

evaporation losses). This same action can occur in the winter time as well and should be taken into

account during the winter in cooler climates..16


The earth's basic air envelope is made up of about 78% nitrogen, 21% oxygen, and 0.03% carbon

dioxide. There are also traces of several other elemental and molecular gasses but they will be ignored

since they have no known effects within the pond environment. Concentrations of these gases within

water is a whole different story. The concentrations are much smaller and are measured in milligrams

per liter (mg/l) or somewhat equivalently, in parts per million (ppm). A typical pond at a temperature of

70 O F. will have concentrations of about 13 mg/l nitrogen, 9 mg/l oxygen, and 35 mg/l carbon dioxide.

As the air components dissolve into the water, a point is reached where no more can be added. This

point is called saturation. The saturation points are different for each of the gases and are dependent

upon several different factors but temperature is the most important. As the temperature increases, the

water simply cannot hold as much of each type of gas. For oxygen, (See figure 2.) the approximate

saturation level at 50 O F. is 11.5 mg/l; at 70 O F., 9 mg/l; and at 90 O F., 7.5 mg/l. Impurities added to the

water (i.e. salt) or an increase in altitude (above sea level) further decrease these saturation levels. Four

pounds of salt per hundred gallons of water (5 ppt) will decrease the oxygen saturation levels about 1


Fish are remarkably well adapted for extracting oxygen from the very low concentrations found in

water. The rate of oxygen consumption by Koi is closely related to the water temperature. Koi are "cold

blooded", that is, their body temperature is essentially that of their environment. Their metabolic

activities are basically enzyme-catalyzed chemical reactions that are temperature dependent. The.17

metabolism and activity increase with temperature which increases their oxygen demand. There is both

an optimum and maximum temperature at which the Koi live and function. At optimum temperature,

oxygen consumption is high because of rapid growth and significant activity. Above this optimum

temperature, the fish start to experience stress. This stress triggers their warning and defense systems

which require a very high oxygen consumption. Unfortunately, as we saw above, the amount of oxygen

available in the water also decreases with temperature. The combination of these two events normally

limit the maximum temperature at which the Koi can survive.


The minimum limiting oxygen concentrations for a fish is dependent upon its genetic makeup, water

temperature, level of activity, long term acclimation, and stress tolerance. Water with an oxygen

concentration of less than 3 mg/l will generally not support fish. When concentrations fall to about 3-4

mg/L, fish start gasping for air at the surface or huddle around the water fall (higher concentration

points). Bio-converter bacteria may start to die, dumping toxins into the water and compounding the

lack of oxygen to the fish. Levels between 3 and 5 mg/l can normally be tolerated for short periods.

Young Koi are less tolerant of low oxygen than the older, larger ones although the larger ones consume

considerably more oxygen. Above 5 mg/l, almost all aquatic organisms can survive indefinitely,

provided other environmental parameters are within allowable limits. Whereas the fish are reasonably

comfortable and healthy at 5-6 mg/L concentrations, many people consider the efficiency of the bio-converter

to be at maximum only when the water entering the bio-converter media is near oxygen

saturation. Ideally, our ponds should be at or near oxygen saturation at all times.


Pill, powder, and droplet (or combination) test kits are available. Most involve three steps and a final

color metric chart. Recommended test kit range 0 - 15 mg/L. Note: Some test kits can show false

readings if various chemical treatments are in the water. Electronic dissolved oxygen meters are also

available. These are accurate and convenient, but quite expensive. A dissolved oxygen test kit is

considered nice to have but not required for the average pondkeeper.


Whenever air is in contact with the water, whether through natural or artificial means, a transfer of

oxygen from the air to the water takes place until the water becomes saturated. Plants under light convert

carbon dioxide to oxygen in the water. Fish, plants at night, and aerobic bacterial action consume the



It is not difficult to get all the air into the water that the fish need. Oxygen is continually transferred into

the water at the surface of the pond and normally only a small water fall will bring the pond water to or

near to saturation. Heavily populated ponds may need supplemental air and ponds with a large amount

of algae may need supplemental air at night when the plants are not making oxygen but consuming it. It

is very important that sufficient circulation is provided within the pond so that all areas have proper


Well water often has almost no oxygen content. When adding well water to a pond, use a fine spray

nozzle over the surface of the pond or a great deal of agitation to add oxygen to the makeup water.

Almost all of the oxygen dissolved into the water from an air bubble occurs when the bubble is being

formed. Only a negligible amount occurs during the bubbles transit to the surface of the water. This is

why an aeration process that makes many small bubbles is better than one that makes fewer larger ones.

The breaking up of larger bubbles into smaller ones also repeats this formation and transfer process.

A "sheet" type waterfall can provide more dissolved oxygen in a pond than the "cascade" type waterfall

whose velocity is low when the water finally enters the pond. Although the cascade type waterfall

provides better aeration of the water that is entering the pond, the sheet type provides better aeration of

the water that is already in the pond. The sheet of water tends to shear the larger bubbles of air formed at

surface entry into smaller ones below the surface. This action can occur at depths of up to three feet or

more and result in oxygen transfer to a much larger amount of water than just that which is entering the

pond. For most situations, the amount of water flow is determined by filtration requirements and either

type will be more than sufficient to maintain the pond oxygen levels at or near saturation.

A common method of providing additional oxygen to the water is through the use of an eductor type air

jet (sometimes called a venturi). An added advantage of this device is that it can simultaneously provide

improved circulation of the pond water.

Air stones or similar bubble forming devices driven by an air pump can also be used to provide

supplemental air. A single air stone can supply sufficient air for up to a 1000 gallon pond although pond

water circulation problems may still exist. It is recommended that a backup air pump with tubing and air

stones (size and quantity depending on pond size) be kept on hand in case of main water pump

malfunctions. This could also be used to supply air to an isolation tank if needed. In an emergency, just

splashing the water by hand or with a bucket can add enough oxygen to sustain the fish (particularly in a

small pond) until the problem is corrected.

When a power loss or other malfunction causes water flow to stop and hence most aeration to also cease,

several problems develop. The oxygen concentration drops and ammonia starts building up. The size

and population density of the pond will determine how long before this becomes a problem but the

bacteria in the bio-converter will start dying off at about the 4 hour point without circulation. After about

4 hours, it is important that before flow through the bio-converter is restored, it should be drained to

remove any toxins released by the dying bacteria. The ammonia levels and nitrite levels should then be

monitored closely for the next few days.

Note how this implies the importance of oxygenated water being circulated through the filter 24 hours a

day. The pumps moving water between the pond and the filter system should never be shut off except

for short periods during maintenance. If the pond design includes water features such as fountains or

large water falls that are desired to be shut off at times, they should be provided with a pump separate

from the filtration system pump..19

Oxygenation During Transport

When plastic bagging fish for transport, use only enough water to just cover the dorsal fin. Ensure the

bag is of sufficient size that the fish can have an inch or more space from the sides and ends of the bag

(and sufficient strength to support the weight of the water and fish. 3-4 mil thick bags are normally

used). Squeeze out the current air, add 5-10 times the amount of oxygen as water. This is normally

sufficient oxygen for up to 24 hours. If oxygen is not available, just the air in the bag is sufficient for an

hour or so.

Ammonia build up and temperature control then become the major problems. Placing the bags in a

Styrofoam picnic cooler can help maintain temperature controls. Cover the top of the box that the bags

are in. The darkness soothes the fish a bit and thus decreases the ammonia generation. If transporting in

a car, put the cooler in the passenger compartment, not the trunk. This is of more importance during the

summer than winter but applies to all times. Do not leave them in a locked car while stopping for lunch,

use a fast food drive through.

Based on reported controlled experiments, it was found that floating transport bags in the pond for 30

minutes prior to release slightly decreased the mortality rate, particularly for small fish. This test was

conducted with the fish bagged for one hour. For fish that had been bagged for four hours, it was found

that the mortality rate increased slightly for all sizes of fish if the bag was floated for 30 minutes. My

recommendation is that if the fish have been bagged for four or more hours, and the temperature

difference between the transport water and pond water is less than 10 degrees, it is better to release them

immediately than to subject the fish to the "bad" water in the bag for an additional half-hour. Thirty

minutes of floating will prevent some shock if the temperature difference is large, but it will not

acclimatize the fish to the new temperature. Actual temperature acclimation of a fish takes several days,

similar to us dealing with jet lag. It is not only the temperature the fish needs to be accustomed to but

also the pH, hardness, alkalinity, "the taste", etc. of it's new surroundings.

Remember the relationship between pH and ammonia toxicity? When the fish are in their sealed

transport bags and expelling carbon dioxide, it causes the pH to drop. This makes the ammonia less

toxic. I have made measurements of fish bagged for over 24 hours and found pH readings below 5.0

with ammonia concentrations over 12 ppm. Yet the fish were in very good condition. When floating a

bag, do not open the bag until ready to release the fish and DO NOT MIX ANY POND WATER

WITH THE TRANSPORT WATER. Just opening the bag can release some of the built up carbon

dioxide thus raising the pH, and even worse, mixing pond water into the transport water can suddenly

raise the pH to where the ammonia is highly toxic. Bottom line is never add pond water to transport

water and never add transport water to pond water.

If a transport tank is being used for moving fish, an air stone or aeration column can be used. A venturi

(air jet) is not recommended since the strong currents induced require the fish to "work" harder which

increases both the oxygen consumption and, of more importance, the ammonia waste products in the

small tank. An air stone can be fed directly from bottled oxygen or from a small air pump. An aeration

column can be fed from a small submersible water pump ideally located at the opposite corner or end.20

from the aeration column. Fish can be transported more safely in a sealed, oxygenated bag than in a

transport tank.

CAUTION: Make sure that the transport tank's air supply cannot be contaminated with

the vehicle's exhaust. Carbon Monoxide is very soluble in water and can be even more

deadly to the fish than to you..21


Common salt, sodium chloride, NaCl, has been termed "The KOI Wonder Drug". A misnomer perhaps,

but salt is a proven staple in the health care and maintenance of Koi worldwide. Koi maintain an internal

concentration of salt in their body fluids higher than that of their liquid environment. Osmosis causes

water to transfer from the lower salinity of the pond water into the tissues of the fish. This additional

water build up must be eliminated by the kidneys. Although salt in higher concentrations may slow

some disease causing bacterial growth in the pond, the predominantly accepted theories ascribe the

primary benefits of salt to lowering the osmotic pressure. This reduces the effort the fish must expend in

eliminating the excess water. The saved energy is then available for use by the fish's own immune

system to take care of other potential problems. The presence of salt also helps counteract any nitrite

toxicity. In some cold climate areas, it is added in the Winter to lower the freezing point of the water.

Salt can cause pond plant damage as the concentration increases. Floating plants, (water hyacinth, water

lettuce, etc.) are affected at lower concentrations than most bog plants. Related, salt may provide some

minor control of algae in the higher concentrations.

The amount of salt dissolved in water is termed the salinity and is measured either as a per cent, in parts-per-

thousand (ppt), or in parts-per-million (ppm) (where 10 ppt = 1% = 10000 ppm). The more common

parts-per-thousand measurement is the weight of the salt in pounds per thousand pounds of water (about

125 gallons). Pond-keepers often talk about the pounds of salt per hundred gallons of water. Since 100

gallons of pure water weighs about 800 pounds, one pound of salt per hundred gallons equates to a

salinity of 1.25 ppt (0.125% or 1250 ppm). (1 ppt = 0.8 pounds per hundred gallons)

[Note: Koi internal fluid salinity is on the order of 9 ppt (about the same as ours). Sea water is around 35

ppt to 70 ppt depending upon geographical location. The Great Salt Lake has a nominal concentration of

about 250 ppt.]

There is some disagreement about salt in Koi ponds. Our San Diego tap water often has a salinity of up

to 0.5 ppt. This amount cannot be tasted but we drink it and we put it into our ponds as make up water. If

our Koi were put into an absolutely pure (distilled) water environment, the osmotic pressure would be so

high that some would be unable to eliminate the excess water and would die almost as if by drowning.

On the other hand, if the salinity approaches that of the internal tissues of the fish, the osmosis process

will decrease or even reverse. This can cause the fish to die, essentially of dehydration. Any discussions

should therefore center not on should salt be in the pond but how much.

Salinity acceptable range: 0 - 5 ppt

The addition of one to two pounds of salt per hundred gallons of water (1.25-2.5 ppt) is recommended

for most ponds, especially in the Spring and Fall. This is a fairly conservative dosage but unless one has

an accurate measurement method, higher concentrations should be avoided. If nitrite is present, two

pounds of salt per hundred gallons is appropriate to reduce the nitrite toxicity. After the initial

application, the dosage applies ONLY to the amount of water being taken out and replaced, NOT to the.22

amount of water in the entire pond, and NOT to water being added to replace that lost by evaporation.

Except for very short-term medicinal baths at concentrations often around 25 ppt (1 pound per 5

gallons), and administered under tightly controlled conditions, it is not recommended that Koi be

subjected to a salinity exceeding 5 ppt (4 pounds per hundred gallons), especially for extended periods.

Salinity levels are normally maintained by the addition of salt to increase it and by water change outs to

decrease it. Introduce the salt, if possible, at the discharge side of the bio-converter (not at the bio-converter

inlet nor directly into the pond). If the addition must be made directly into the pond, dissolve

the salt in a bucket of pond water and distribute it evenly around the edges of the pond. Inquisitive Koi

will check to see if any new addition to the pond might be something to eat. Although they will probably

not swallow the pieces of salt, direct contact of crystalline salt with the fish for more than a few seconds

can cause injuries similar to burns. When making the initial or any large application, it is probably better

to divide it into two to four daily partial additions rather than putting it in all at once. Inexpensive and

quite pure solar-dried or kiln-dried salt used in home water softeners is available at most supermarkets

and home improvement centers. Do not use pelletized water softener salt that has binding agents or any

type of iodized salt.

The floating hydrometers that are used to measure the salinity of salt water aquariums will not supply

the accuracy necessary for use in a Koi pond. Electronic conductivity meters will give an indication of

the amount of salt but can give false readings due to other substances in the water. A chemical test kit is

available from LaMotte that is designed to measure 0-20 ppt. By increasing the sample size by four and

dividing the reading by four, the kit can be used to measure our desired range of 0-5 ppt. Aquarium

Pharmaceuticals also has an inexpensive salinity test kit available that is quite accurate over the

designed range of 0-2.4 ppt. The water sample can be mixed with an equal amount of distilled water and

then multiply the reading by two to extend the range to 0-4.8ppt.

A salinity test kit is not considered to be a requirement for the average pond but one should be used if

attempting to maintain salinity levels above 4 ppt.



Chlorine (Cl), measured in ppm, is a gas which has been added to tap water to control harmful bacteria.

City provided tap water is normally found to have 0.5 - 3.0 ppm but higher surges are sometimes

observed. Some city water supplies can still be found that either do not require chlorination or may have

the chlorine removed before the water is distributed. This would not be of concern to those who take

their tap water directly from a private well. Droplet and pill test kits are available. Recommended test kit

range 0 - 4 ppm. A chlorine test kit is not considered necessary for the average pond.

Acceptable concentration 0


Chlorine is a quick killer in fairly low concentrations (less than 0.5 ppm). Even in very small

concentrations, it burns the edges of the gills with long term after effects. It also can be deadly to the

bio-converter bacteria..23


In an open container, water will release about 1/4 of the chlorine concentration per day to the air . Water

that has set in an open container for a week or just for a couple days if aerated, is normally safe to use or

better yet, pretreat tap water with one of the commercial chemical products. Follow the manufacturer's

directions (Or make your own).

Homemade Chlorine Neutralizer

Make a solution consisting of 4 ounces (1/4 lb) Sodium Thiosulfate crystals (photo or technical grade)

dissolved in 1 gallon of distilled or deionized water. Use 5 ml (1 teaspoon) of the solution for each 10

gallons of makeup water to neutralize up to 3.75 ppm chlorine. One cup can be used for each 500

gallons. (The entire one gallon of solution will treat about 7500 gallons of tap water.) The shelf life of

the solution is about six months when stored in a cool location. The crystals will keep for several years if

kept dry.

When pretreating replacement water, the dosage is for the quantity of water being replaced, not the total

pond capacity! Although it would be better to treat all tap water being added, small amounts of

replacement water without dechlorination treatment are often added without noticeable effects to the

fish. It is recommended that any time more than one percent of the pond water is being added, it be

treated. Do not use chlorinated tap water to clean your bio converter (filter) media unless you are

actually trying to sterilize it. Water from the pond is a much better choice for this task.


Chloramine is a compound of chlorine and ammonia that is also added to tap water to control bacteria. It

can also be formed by adding water containing free chlorine to a pond containing ammonia. If any

ammonia is present in a pond, be sure and treat it before adding any tap water containing chlorine. To

determine if chloramine is in your tap water, fill a 5 gallon bucket with tap water, add the proper amount

of chlorine neutralizer, and then test the water for ammonia using your ammonia test kit. Chloramine is

present if a positive indication of ammonia is found. Chloramine is difficult to measure quantitatively in

low concentrations, and particularly when a combination of chlorine and chloramine is present.

Acceptable concentration 0

Chloramine does not decrease concentration nearly as fast as chlorine when exposed to air. It produces

the same general effects as chlorine but is usually found in the lower concentrations that result in long

term damage to the fish. The same treatment actions as for chlorine apply except that the ammonia

remains after neutralization. A "healthy" bio-converter will take care of the ammonia or a chemical

treatment may be used. Some commercial products incorporate treatment to both neutralize the chlorine

and bind the ammonia components at the same time. Check the manufacturer's directions..24


Partial water change outs can reduce the amount of anything dissolved in the water but not totally

remove it. Although it is sometimes necessary, draining and refilling a pond should only be used as a

last resort! Do not use large water change outs to clear green water conditions. A large water change out

will normally make the situation worse, not better. Often, several partial water change outs, performed

over a period of days or even weeks, can reduce the concentration of an undesired item to acceptable

levels without serious after effects. A water change out reduces the amount of a substance in the water

by the same amount as the percentage of water replaced. Remember the concentrations of any "good"

stuff in the pond is being reduced at the same time as the "bad" stuff. Also the water being used for

replacement may have undesirable components as well.

A water change out is considered to be when a measured amount of water is removed from the pond and

then replaced. Just adding water and letting the pond overflow will not accomplish the desired results

unless significantly more water is transferred. Water added to replace that lost by evaporation is not part

of a change out.

Example: It is desired to decrease the Salt in a pond by one half. Any of the following will have the

same approximate result:

a. Seven successive 10% change outs.

b. One 25% change out followed by four 10%.

c. Two successive 25% change outs followed by one 10%.

d. One 50% change out.

Depending on the urgency to carry out the action, the largest number of change outs over the longest

time would be the best approach.

Unfortunately, this does not apply in the same way to pH. The change in pH for a given water change is

dependent upon the Alkalinity and pH in the pond as well as the Alkalinity and pH of the replacement

water. Adding water with a higher pH than the pond water will raise the pond water pH but it is difficult

to predict how much. Remember that if the water being added to the pond has a pH higher than that of

the pond, make sure any ammonia in the pond has been treated before adding the new water.

It is considered appropriate to change out from 5 to 10 percent of a pond's water per week. A small pond

(500 gallons or less) should receive the 10% weekly change out. The 5% change out is appropriate for

larger ponds (5000 gallons or more). Any water replaced after a back flush of a filter system or other

maintenance actions can be included as being part of this weekly change out amount.

It is very common for pond keepers to skip making these routine water changeouts. After all the pond is

full of water. Why should we just dump some of it and refill it? Many components in the water build up

over time and this is the only way to reduce them. Experienced pond keepers know that their fish are

healthier and stronger when these water changeouts are conducted..25

When making the water replacement with tap water that contains chlorine and/or chloramine, it would

be better to pretreat the water with the chlorine neutralizer before adding it to the pond (particularly

small ponds). If this cannot easily be done, use a fine spray of water over the pond and divide the total

computed neutralizer dosage into two to four parts and add while the makeup water is being added.

Don't Forget To Turn Off The Water! Set a timer or do something to remind you that makeup water

is running into the pond. Inexpensive flow timer shutoff devices that hook directly on the hose are

available and are a good safety item to use..26


Although it is sometimes called an algae bloom, normally the names it is called are unprintable. For

some, it seems to happen every Spring (also sometimes in the Fall). For others, it is almost a way of life.

A limited number of pond keepers have never or rarely experienced this "wonder" of nature. It is said

that the Koi thrive in it, but you cannot see them to tell if they are thriving or not. You have heard many

reasons why your water turns green and tried assorted mechanical wizardry and various chemical

concoctions to clear it, (which may or may not have been harmful to your Koi), but it is still green.

There is a lot of "snake oil" out on the market to clear green water.

Green water is caused by an excessively large number of tiny organisms in the water. Called

phytoplankton, these minute plants are part of the algae family that has thousands of distinct species

found in water (and ice) throughout the world. These organisms are very small, with the most common

ones found in our ponds being around 15 microns (0.0006 inches) in diameter. All pond water contains

large numbers of different kinds of these plants and other microorganisms. Water that appears to be

crystal clear just doesn't have as many.

Some of the statements that follow are somewhat controversial, but they are based on several years of

research and experimentation dealing with the subject. From this research, I have concluded that within

our biologic converters, a third group of bacteria exist. When these heterotroph bacteria consume dead

algae in an aerobic environment, they release an enzyme, possibly used to help them digest the dead

algae. The flow of water through the media carries surplus amounts of this enzyme back into the pond

where it Akills@ off the other algae.

This enzyme appears to be effective against many species of string algae as well as the bloom algae. It

does not seem to have as much effect on the string algae which is only partially submerged or within a

high flow area, i.e. in a splashing brook or around a waterfall. This may have to do with contact time

requirements. The short blackish-green mat algae found on the walls of a "healthy" pond is composed

primarily of dead string algae which is also believed to be a result of control by the antibiotic. Further,

this mat area may also be providing a portion of the enzyme as it is being broken down by the

heterotroph bacteria.

This seems to explain what we see in our ponds much better than many of the traditional myths which I

believe arise from invalid extrapolations and application of true scientific findings based on studies of

large lakes and oceans. Most of these findings just simply do not apply to the essentially closed

environment of an established, circulating Koi pond. We will discuss only two of the myths here. For

more and a detailed description of the experiments leading to these conclusions, see my article in the

Mar-Apr 1998 issue of KOI USA.

MYTH: Pond algae blooms are primarily related to various nutrient concentrations in the water such as

nitrate and/or phosphate..27

FACT: There is no evidence to substantiate any relationship between nutrient levels and the inception or

termination of the common algae blooms in most Koi ponds. Quite to the contrary, the measurable

nutrient levels are normally so high, most questions should be why the algae bloom is not continuous.

Commercial laboratory analysis consistently show very high concentrations of all required nutrients.

These concentrations are much higher than could be expected to prevent such an event. Further, most of

these levels actually show a slight increase after a heavy bloom subsides.

MYTH: Providing shade over the pond will prevent an algae bloom.

FACT: It is true that algae needs light to grow and reproduce. But what is interesting is the small

amount of light that is actually required. Controlled experiments using reduction in sun light of 90% still

show significant algae growth. There are many examples of ponds that are heavily shaded but quite

green and just as many others with direct sun exposure that have no algae bloom problems at all. There

have been positive results reported of completely covering a pond suffering from green water with an

opaque plastic cover for 5-10 days. I'm not too sure what the Koi think about this but it is obviously not

an acceptable permanent solution. I do recommend providing shade over a pond, but more for

temperature stability than for algae control.

So, what is the solution? It seems to be simply a properly sized biologic converter and a proper flow rate

of oxygenated water through it. The bio-converter must be large enough to support the heterotroph

bacteria colonies which need considerably more space than just the nitrification bacterial colonies. This

has led to two rules of thumb. The first is that the amount of water in the pond and filter system should

be circulated through the bio-converter at least once per hour. Second is that a flow rate of

approximately 150 gallons per hour per square foot of media should be used. As an example of a 1500

gallon pond, we should be moving 1500 gallons of water through the bio-converter each hour and the

bio-converter cross sectional area exposed to water flow should be 10 square feet. The thickness of the

media is determined by the media selection.

Bubble bead or similar type pressurized filters do not generally have sufficient internal surface area to

support the heterotroph colonies necessary for the enzyme production although they can provide the area

necessary for the smaller nitrification colonies. They do an excellent job of capturing the dead algae and

other solids. During the frequent backwashing processes, however, the dead algae and much of the

heterotroph bacterial colonies are removed from the system giving insufficient time for the enzyme to be

produced. This is why ponds using these type filters almost always require an ultraviolet system to

handle the green water problem. A properly sized UV system will do a good job on eradicating the

bloom algae. It will not affect the string algae, only the phytoplankton that actually pass through the

unit. There are also some indications that the UV radiation may destroy or at least weaken any enzyme



This catch all category of pollutants means anything added to the pond that is not wanted in the pond.

Pollutants can consist of items which may or may not be harmful to the fish and they may or may not be

visible. They may float on the surface, sink to the bottom or dissolve into the water. They may come

from outside the pond or from within the pond itself, i.e. oil leaking from a submerged pump. Some

pollutants are easy to identify and control and/or remove, i.e. leaves, pollen, dead rats, etc. Some just

add to the filter load if not removed but cause little other problems if not in excessive amounts, i.e. bird

droppings. Most of the harmful pollutants that dissolve into the water are hard to identify or quantify.

Surface water runoff that can enter the pond is often a major source of pollutants. This is why all ponds

should be designed with a raised edge or at least some type of channel around it so that the surface water

will not enter the pond. Any roof runoff from adjacent buildings should also be controlled. Other than

preventing these pollutants from being introduced into the pond, they can only be controlled through

water change out procedures.

Here in sunny southern California, where we get very little rain over long periods of time, heavy

buildups of "stuff" on the covers, shade cloth, plants, or trees hanging over our ponds often occur. When

it does rain, all of a sudden there is a large amount of this material that is washed off and added to the

pond water with possible detrimental effects. (We are all familiar with oil coming up from the roadways

during a rain following a dry spell and how the cars go slip-sliding down the interstate.) If the material

overhanging the pond is rinsed off with a hose every couple of weeks, then the individual additions are

much smaller and are more easily controlled through the routine water change outs. This rinse down of

overhanging material should be part of each pond keeper's routine pond maintenance (at least montly)..29


One pollutant area that is often overlooked by pond keepers has to do with the plants in the pond or

those that are part of the landscaping around (and over) the pond. The seeds of most plants can swell and

plug up the digestive tract of the Koi. A partial list of the plants or parts of plants that have been reported

as having some toxicity to Koi (and pets and people) for various reasons include:

Amaryllis - bulbs Baneberry - berries, roots Bird of Paradise - seeds

Black Locust Bark -

sprouts, foliage

Boxwood - leaves, stems Buttercup - sap, leaves

Calla Lily - leaves Cherry - bark, twigs, leaves, pits Coral Plant - seeds

Daffodil - bulbs Datura - berries Death Camas - all parts

Eggplant - all but fruit Elephants Ear - leaves, stem English Ivy - berries

Foxglove - leaves, seeds Hemlock - all parts Holly - berries

Hyacinth - bulbs Indian Turnip - all parts Iris - bulbs

Jasamine - berries Java Bean - uncooked bean Lantana - immature berries

Laurel - all parts Locoweed - all parts Marijuana - all parts

Mayapple - all parts Mistletoe - berries Mock Orange - fruit

Morning Glory - all parts Narcissus - bulbs Oak - acorns, foliage

Pine - sap Poinsettia - leaves, flowers Potato - eyes, new roots

Privet - berries, leaves Prunus varieties - seeds, some Redwood - sap (from decks also)

Rhubarb - leaves Ranunculus - all parts parts Snapdragon - all parts

Snowdrop - all parts Tiger Lily - all parts Tomato - leaves

Tulip - bulbs

Have you identified all the plants in, over, and around your pond?.30


Keep good records of your pond. A chronological log of chemical test results, treatments, maintenance

actions, water change outs, and even addition or removal of fish can help determine the cause (and

required treatment) of a future problem. I keep mine in a computer file but just a simple notebook is all

that is needed.

Keep chemical test apparatus clean. Scrub out the test vials periodically. Just rinsing with pond water

doesn't get out all the residue buildup. Whenever you buy a test kit, write the purchase date on it. If not

otherwise stated on the test kit, replace any liquid based test kits every year. Replace the sealed packet

dry powder and pill based kits every two years.

Be careful about anything that you put in your pond! Know your pond capacity and carefully

calculate and measure dosages. Know what you are treating for; it is usually better not to treat at all than

to dump in something because you think there might be a problem. Second only to ammonia poisoning,

more Koi have died from improper treatment with medicines and chemicals than for any other reason.

Many times, the first indication of a problem can be detected by simply watching the behavior of the

fish. Changes to their normal activities means it is time to get out the test kits. This is the best part of

having the pond anyway so spend some quality time with your Koi and get to know them..31

Approximate Conversion Factors

1 fluid ounce = 1.04 ounces (avoirdupois) = 29.5 ml

1 ounce (avoirdupois) = 28.35 grams

1 lb = 16.0 ounces (avoirdupois) = 454 grams

1 gallon = 4 quarts = 8 pints = 16 cups = 128 fluid ounces

1 gallon = 231 cu in= 8.33 lbs (pure water weight) = 3.79 liters

Note: 1 English (Imperial gallon) = 1.2 U.S. gallons

1 quart = 2 pints = 4 cups = 32 ounces = .945 liters

1 pint = 16 ounces = 2 cups

1 cup = 8 ounces = 16 tablespoons = 236 ml

1 tablespoon = 3 teaspoons

1 teaspoon = 5 ml = 110 drops (depends on dropper)

1 gallon/hr = 3.82 cu in/min

1 gallon/minute = 60 gallons/hour

1 gallon/second = 60 gallons/min = 3600 gallons/hour

1 ton = 2000 pounds = 240 gallons of water

1 pound per hundred gallons = 1200 ppm = 1.20 ppt = 0.120 %

1 foot = 12.0 inches = 0.305 meters

1 yard = 3.00 feet = 36.0 inches = .914 meters

1 mile = 5280 feet = 1.61 kilometers

1 acre = 4356 square feet

1 cu in = 0.00433 gal = .0164 liters = 16.4 ml

1 cu ft = 1728 cu in = 7.48 gal = 28.3 liters

1 liter (l) = 1000 milliliters (ml) = 0.001 cu meters = 0.264 gal = 61.0 cu in

1 liter/hr = 1.02 cu in/min

1 meter = 100 centimeters = 3.28 feet = 39.4 inches = 1.09 yards

1 centimeter = 10 millimeters

1 micron = 0.000001 meters = .0001 centimeter

1 kilometer = 1000 meters = 0.621 miles

1 ml water = 1 gram = 1 cubic centimeter

1 kilogram (kg) = 1000 grams (g) = 1000000 milligrams (mg) = 2.20 lb

1 percent (%) = 10 parts per thousand (ppt) = 10000 parts per million (ppm)

1 ppm = 1 mg/l = 1 pound per 120,000 gallons = 1 ounce per 7500 gallons

1 minute = 60 seconds

1 hour = 60 minutes = 3600 seconds

Temperature Fahrenheit <=> Centigrade O F = 9/5 O C + 32 O C = ( O F - 32) 5/9




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Last modified: 07/07/15.