Nitrate is the final product from the breakdown of ammonia released by the fish.
Nitrate is not especially harmful to freshwater fish but is a potent plant fertilizer and can contribute to the growth of unsightly and unwelcome algae, such as green water or blanketweed. Ideally, the levels of nitrate in the Koi pond should be controlled to help reduce the likelihood of these unwelcome algae blooms occurring. It is recommended that a Nitrate Test Kit is used to determine the quantity present in the pond and control the concentration through water changes.
Summer usually means increased pond water loss due to evaporation, which of course leads to topping off our ponds more. You should always add dechlorinator when topping off the water level of a pond. Any amount of chlorine (such as that found in treated water) can be harmful to your fish. Even if it is not enough chlorine to mean immediate death of the fish, this chlorine can still cause harm to proper gill function.
