Ammonia Test Kit – Fresh/Salt water. Taking a few minutes each week to maintain and monitor aquarium conditions is the key to a healthy aquarium. Tropical fish continually release ammonia into the aquarium through their gills, urine and solid waste. Uneaten food and decaying organic matter also add ammonia to the water. Even small amounts of ammonia stress fish; large amounts of ammonia will kill fish. Ammonia is the number one killer of tropical fish.