Fluval Nano Aquarium Underwater Filter. Fluval Nano Aquarium Filter is an optimal water filtration system for small aquariums up to 55 litres (15 US gal). Equipped with foam filter media, it provides effective and thorough mechanical and biological filtration. A fine foam pad traps small debris and a Bio-Foam captures debris and houses nitrifying bacteria. The filter also provides the option of adding a carbon cartridge (sold separately) for additional chemical filtering. The Nano Filter has an adjustable flow output with an attachable spray bar that distributes a gentle, even flow of water, making it safe for delicate fish or shrimp. Foam media provides both mechanical and biological filtration Fine foam pad traps debris, while Bio-Foam provides ideal surface for growth of beneficial nitrifying bacteria Carbon cartridge offers additional filtering option to remove odors and impurities (Replacement Carbon Cartridge) Adjustable flow output with attachable 360 swivel spray bar distributes a gentle and even water flow – safe for delicate fish or shrimp Quickly assembles/disassembles for easy installation and maintenance 3 suction cups offer secure in-tank attachment Great for small fish, betta, and shrimp.