Keep your aquarium free of harmful ammonia with AquaClear Ammonia Remover Filter Insert. Fish waste， uneaten food and other refuse can cause ammonia to build up in your aquarium which can cause stress， illness and even death. AquaClear Ammonia Remover Filter Insert works immediately to remove and help control ammonia and nitrite， improving your water quality and reducing stress on your fish. It is ideal for new or heavily populated freshwater aquariums.