Help remove odors and impurities from your aquarium with Fluval's Nano Carbon Filter Cartridge. Fish waste， uneaten food and other organic matter can build up in your aquarium water causing odor， discoloration and impurities like ammonia and nitrates， which can be harmful to your finned friends. Specifically designed to load easily inside the Fluval Nano Filter， this cartridge contains highly porous carbon that works to adsorb odors， discoloration and impurities. Fluval cartridges help you maintain the quality of your aquarium water for the health and well-being of your finned friends.