Specifically designed to fit inside the Fluval Nano Filter, the Fluval Nano Carbon Cartridge Filter Media Insert contains highly porous carbon that effectively adsorbs odors, discolorations and impurities. The Fluval Nano Carbon Cartridge Filter Media Insert's large 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.