What is ammonia?

Ammonia is excreted by the fish as a waste product. It is extremely toxic to the fish, and is broken down into less toxic nitrite by the beneficial bacteria in the filter of your aquarium. Ammonia is most toxic to fish when the pH is alkaline and temperature is high, so it is most dangerous in cichlid or marine aquariums.

Why test for ammonia?

Any ammonia present in the aquarium water will cause major health problems for the fish. Toxic ammonia can build up in aquariums where there are not sufficient beneficial filter bacteria to deal with the total waste from all the fish in the aquarium. This situation can commonly arise in new aquariums, when new fish are added, when the filter bacteria have been disrupted (e.g during cleaning), or during accidental mis-dosing of aquarium medications.