The Aquarium Mini Test Kit from NT Labs is suitable for freshwater aquariums and performs checks on the 3 most important water parameters in an aquarium. The Aquarium Water Mini Test Kit includes tests for pH, nitrite (NO2) and ammonia (NH3). The Kit comes complete with full instructions to help ensure you carry out the tests correctly, and to help restore perfect water quality should a parameter be incorrect. What is ammonia? Ammonia is excreted by the fish as a waste product. It is extremely toxic to fish, but 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 the temperature is high, so it is most dangerous in hard water aquariums.