Ideal for goldfish, the filter cartridge contains zeolite and Ceramitek for optimum filtration and a healthy aquarium. The zeolite effectively adsorbs toxic ammonia and reduces stress on fish, while the Ceramitek, a highly porous ceramic biological filter medium, optimizes biological filtration. The easy-to-use disposable cartridge should be replaced every two weeks for best results. Never replace all filter cartridges at the same time to ensure a constant presence of beneficial bacteria.