Coralife - BioCube Filter Cartridge 2 Pack
BioCube Aquariums include a two-stage filter in their back chamber. These disposable cartridges provide both mechanical and chemical filtration for clear, debris-free water. The poly-woven pe-filter traps free-floating materials and waste while the activated carbon removes odors and discoloration. Each pack comes with two filter cartridges.
Rivers to Reef says: Don't let these guys clog up too badly or you might run into nitrate problems. We recommend, depending on your tanks bio-load, replacing them every 3 or 4 weeks.