The AquaClear AC20/30 Ammonia Remover Insert is ideal for new or heavily populated freshwater aquariums. It removes and controls harmful ammonia and nitrite to create a healthy aquatic environment. Controlling ammonia levels is also critical for reducing stress on fish. For the AquaClear AC20 Power Filter and AquaClear AC30 Power Filter. The Product Manual recommends you replace the Ammonia Remover Insert every month. 1-pack.