For the ultimate in convenience and quiet, choose a Tetra Internal Filter. This filter mounts on the inside of the aquarium, rather than hanging from the outside making it possible to place the tank flush against a wall. The 13i InternalFilter uses air bubbles to move water up the airlift tube and through the filter cartridge making it ideal for keeping small fish and breeding fish. The Tetra Internal filter adjusts easily to high or low water levels with mounting suction cups and/or bracket. Each unit includes the filter, air pump, two feet of airline tubing and one Small Tetra carbon filter cartridge. For Aquariums up to 3 gal.