Marina Bio Clear Cartridge for Slim Filters 36pk (12 x 3pk) 36 total Bio-Clear replacement cartridges for Marina Slim Power Filter Ideal for goldfish, they contain zeolite and Ceramitek for optimum filtration Zeolite effectively absorbs toxic ammonia and reduces stress on fish in your tank Ceramitek, a highly porous, ceramic biological filter medium, optimizes biological filtration to support the growth of good bacteria These genuine replacement filter cartridges are specifically designed for use in the Marina Slim S10, S15 or S20 aquatic filter