Marina Bio-Clear Slim Filter Cartridge. The Marina Slim Filter Zeolite Plus Ceramic Cartridge combines Zeolite and Ceramitek in one cartridge for 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. Never replace all filter cartridges at the same time in order to ensure constant presence of beneficial bacteria. The Marina Slim Filter Zeolite Plus Ceramic is best used in goldfish aquariums. Absorbs toxic ammonia and reduces fish stress Contains Ceramitek, a highly porous ceramic biological filter medium 3-pack; Easy to replace Fits the Marina S10, S15 and S20 Slim Filters Size : 3 Count