Marina Bio-Carb Slim Filter Cartridge. The Marina Slim Filter Carbon Plus Ceramic Cartridge combines activated carbon and Ceramitek in one cartridge for a healthy aquarium. The activated carbon effectively removes pollutants and odors, 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. Make sure to never replace all filter cartridges at the same time in order to ensure constant presence of beneficial bacteria. The Marina Slim Filter Carbon Plus Ceramic is best for Tropical fish. Absorbs toxic ammonia and reduces fish stress Effectively removes pollutants and odors 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