(3 Pack) Marina Slim Filter Zeolite Plus Ceramic Cartridge, 3 Cartridges each 9 Total Cartridges (3 Packs with 3 per Pack) Marina Slim Filter Zeolite Plus Ceramic Cartridges Absorbs toxic ammonia and reduces fish stress Contains Ceramitek, a highly porous ceramic biological filter medium Fits the Marina S10, S15 and S20 Slim Filters