Fish continually release ammonia into the aquarium through ttheir 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. It is recommended to test water for ammonia weekly. API AMMO-CARB contains a unique blend of high grade activated carbon and ammonia-removing resin, acting as a double filtration system to effectively clean and condition water. The activated carbon removes dissolved organic waste, colors, and odors while the resin removes toxic ammonia. Use AMMO-CARB for starting or maintaining freshwater aquariums, or in ornamental ponds. Use as directed.