Once there are koi in the pond, the water will become polluted by ammonia produced as waste from the gills and anal vent. As time passes, algae and other aquatic plant will decompose and cause further pollution. Water testing is therefore the most important task that a koi keeper undertakes.
The presence of ammonia can seriously damage gill filaments, making the absorption of oxygen from the water difficult. It also reduces the fish's ability to control osmotic balance. Exposure to any quantity of ammonia is undesirable, and prolonged exposure, even to low levels of ammonia, can result in the death of koi.
Toxicity of the free ammonia, part of the total ammonia, increases both warmer and more alkaline as the fish can only tolerate smaller quantities of free ammonia as temperature and pH rises. You should therefore take the temperature of the water and monitor pH levels when you test for ammonia.
Refer to the toxicity chart provided with the ammonia test kit to ascertain its real effect. To reduce the risk of health problems, aim for a test kit reading of zero total ammonia in pond water. A rising ammonia level in an established pond may be due to several causes. Lack of maintenance and overstocking are the most frequent reasons.
A few small koi in a large volume of water will be most unlikely to cause a significant rise, even with an un-established filter. Conversely, when many fish are kept in a relatively small volume of water, a modest increase in feeding regime will push up the ammonia level.
Carry out regular testing while a filter is maturing and during changing weather conditions and when feeding patterns alter. Make appropriate water changes when necessary, until zero ammonia is recorded. At these times, check pH level of top up water before adding it to ensure that it will not unduly affect the water in the pond.