Slim Power Filter - Bio-Carb Replacement Cartridge 3pkSlim Filter Bio-Carb replacement cartridge fits all 3 Slim Filter Models. Ideal for tropical fish, it combines activated carbon and Ceramitek in 1 cartridge for a healthy aquarium. The activated carbon effectively removes pollutants and odours, 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.) . There are 3 replacement cartridges in each package.