Water quality testing is important, especially when you are starting a new fish pond or filter. This is the time when the bacteria in the biological filter are trying to grow and establish the biological filtration action. Ammonia and nitrite will be present in the pond during the initial stage of nitrogen cycle. During this time, risk of fish fatality is high.

Experienced pond keepers will not risk putting in expensive, show grade Koi into the pond until there is no ammonia or nitrite present, as determined by the water quality testing. As fish waste is needed to feed and cultivate the bacteria in the new filter system, most pond keepers will put in small feeder fishes or a few cheap, low-grade Koi to produce the needed waste. It normally takes a few weeks for the biological filter to establish itself. During this time, if the pond keeper controls the number of fish in the pond, amount of fish food given and take remedial actions when water testing shows poor water quality, fish lost can be avoided.

Other times when water testing should be done are when you have recently added more fish to your pond. This is the time when the water parameters will deviate from the norm as the filter adjust to the new load of waste matters coming from the increased population.

Besides ammonia and nitrite, the pond keeper should also test for other parameters like pH, carbonate and general hardness, oxygen level and nitrate.

The pH level is a measure of the acidic or basic (alkaline) nature of a solution. Normal tap water or fresh water should have pH level of 7. Water with a lower pH level is deemed acidic while alkaline water would have higher pH. Chalk, limestone, coral or seashells dissolved in water will produce higher pH. pH level is usually determined by your water supply. Koi requires a pH slightly above 7. The best way to control pH is to include crushed coral ships or seashells as one of your filter media. The carbonate in them will acts as a buffer against sudden, sharp drop in pH level which kills fish swiftly.

Oxygen level testing is important to determine if you have enough aeration in your pond to support the fish and plant population in your pond. Do this at the onset of a new pond or when more fishes are added to the pond. Once you have the right level of aeration, the oxygen level seldom fluctuates a lot unless you have a broken pump.

Nitrate is an output of your biological filter. Nitrate is harmless to fish in small quantities but nitrate level should be kept low. When the nitrate level goes beyond the level indicated in the test kit, it means it is time for partial water change. Other symptoms of excessive nitrates will be excessive algae growth (greenish water) or brownish tint in the water.

One other thing is that you should observe your Koi's behaviour daily during feeding. Your water test kits should be used immediately when you notice any Koi behaviour changes. This is a sign that they are not happy with their living environment.