THIS IS TWELVE OF THE THE 2-PACKS (24 Cartridges Total). Replacement BioCube Filter Cartridge, 2-Pack, for all the Oceanic BioCube Aquariums and Coralife BioCube Aquariums. This is the Oceanic 8 BioCube Filter, Oceanic 14 BioCube Filter, Oceanic 29 BioCube Filter, Coralife Size 14 & Size 32 BioCube Filter & Coralife Size 29 & Size 32 BioCube Filter. Coralife recommends, for optimum efficiency, cartridges should be replaced every four to six weeks.