Specifically designed to fit inside the Fluval® Nano Filter, the Fluval® Carbon Cartridge contains highly porous carbon that effectively adsorbs odors, discolorations and impurities. Large amounts of surface area in the carbon effectively remove heavy metals, organic contaminants and pollutants, leaving aquarium water crystal clear and sparkling. The custom designed cartridges easily load into the Nano Filter’s filtration chamber. Package contains 2 cartridges.