Coralife BioCube Original Filter Cartridge Replacements, 2-Pack Replacement BioCube Filter Cartridge, 2-Pack, for all the Oceanic BioCube Aquariums and Coralife BioCube Aquariums This is the Oceanic BioCube Size 8, 14 & 29 Filter, and Coralife Size 14, 16, 29 & 32 Filter If you have a BioCube, this is the replacement filter Coralife recommends, for optimum efficiency, cartridges should be replaced every four to six weeks