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Testing of Pond Water


As hardy as koi are, long term exposure to poor water quality will cause stress and disease. Clear water is not an indication of good water quality Therefore we need to test our pond water periodically rather than wait for disease symptoms to appear.

What to Test For

'A pond is basically a toilet'. Fish waste must not be allowed to accumulate in a pond. At the end of it all, this means a biological filter must be operating properly Fish waste and other organic debris result in the first stage of the nitrogen cycle, a series of events that produce some of the compounds that we test for - ammonia, nitrite and nitrate. Besides that pH value and dissolved oxygen are also important parameters to be tested. Water hardness which indicates the amount of dissolved minerals in the water needs to be tested too.

When to Test ?

Spot tests are important if the pond water indicates a toxic or adverse condition. For example, high ammonia, where corrective action has to be taken immediately Where as it is advisable to test our pond water on a regular basis such as every week and table the results so that trends on direction can be noted early By knowing the direction that the water quality is taking, we can take corrective measure before the problem gets out of hand. If there are major changes to the pond system, such as installing a new filter, major pond cleaning or repair, daily testing of pond water is encouraged to monitor the effect of the change.

Test Kits

Look for user friendly type of test kit which is reliable and easy to use. It is very common to get Home Kit that come with a small container for a measured sample of pond water, a chemical to add to the water sample that will cause the water to change colour. We can then refer to a standard colour chart and compare the results. Most test kit come in either 'Master Pack' which contain several basic test or single test pack. The basic tests are usually ammonia, nitrite, nitrate and pH value.


Ammonia, introduced by fish waste and decomposing organic debris, is the most toxic nitrogen compound. It is present in two forms in the pond - free and ionized. Free ammonia is the most toxic and will cause death in very low concentrations. Problems associated with non - lethal elevated level of ammonia include gill disease, dropsy and finrot. Test kit measure the total ammonia (free plus ionized). With a properly functioning biological filter, the ammonia level is usually zero in the pond and should at least be under 0.1 ppm (mg/l). If the level of ammonia is elevated, make partial water changes and stop feeding the fish until the situation is corrected.


Nitrosomonas bacteria in the filter oxidize ammonia into nitrite, which is less toxic than ammonia, but still bad as it inhibits the ability of the blood to carry oxygen. Our pond may experience a nitrite spike if Nitrobacter colony is not sufficient to oxidize it to nitrate. If the level of nitrite is elevated as shown in our test results, we should make partial water change and if necessary add commercial bacteria high in Nitrobacter to the filter.


Nitrate is the end product of the nitrifying of the nitrogen cycle. It is mush less toxic for koi than either ammonia or nitrite. Nitrate is absorbed as food and fertilizer for algae and is then reduced into free nitrogen by anaerobic bacteria. An oxygenated, clean pond will not have any anaerobic bacteria present, so nitrate will accumulate in the pond. An algaecide is often used to kill or control the algae of which the growth is encouraged by the presence of the nitrate. Partial water changes usually will flush out the accumulating nitrate.


pH indicates the ratio of hydrogen ions to hydroxyl ions on a logarithmic scale from 1 (pure acid) to 14 (pure alkaline). Pure water is 7.0, meaning that there is equal balance of hydrogen ions and hydroxyl ions. Most tap water in Malaysia is around 7.0. Koi do best in water of 7.2 to 8.0. Koi can tolerate a wide range of pH, from 6.5 to 9.0. Even though koi can tolerate extreme of pH there are diseases directly cause by stress. Acidosis is a reaction of fish to acidic condition, in which the fish act highly agitated, with a lot of jumping. Whereas, alkalosis, a reaction to conditions that are too alkaline, will cause the gill and fin to be destroyed. To control pH we can use "pH up" or "pH down" chemical which is available in most fish shop. We can certainly consult experienced koi member or koi dealer for assistance.

Dissolved Oxygen

Dissolved oxygen is usually only a warm weather concern like Malaysia as it is associated with water temperature and algae. The larger the fish, the greater the oxygen demand - low levels will stress and kill our biggest koi. Ponds that have been safe for many years can become a danger as our fish grow larger. Algae takes up oxygen at night, and an algae bloom can cause suffocation in large fish and inhabit the oxidation process of nitrifying bacteria. Dying algae and decaying organic material also takes up oxygen. Testing for dissolved oxygen allow us to determine if our pond has maximum amount of oxygen at specific water temperatures. Splashing the water into small droplets with underwater jets and compressed air installation is a good way of promoting oxygenation.

In conclusion, testing gives us information that we need to ensure the best possible water condition for our fish. It only takes a few minutes a week and is about the best investment you can make. My advice is to contact experience koi member of fish shop for help whenever you have a problem. Do not keep the problem to yourself.


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