The Tetra Whisper 20-40 Internal Filter for aquariums is the ultimate in quiet convenient 3-stage filtration. This submersible 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 and easily hide with tank decor. The air pump (included) provides bubbles that move water through the filter efficiently filtering and oxygenating your aquarium. The water flows through Ultra-Activated carbon absorbing odors and discoloration as well as through the dual-sided mesh of the Bio-Bag Filter trapping debris and fish waste. The Tetra Whisper 20-40 Internal Filter adjusts easily to high or low water levels with a mounting clip. Each unit includes the filter air pump 2 feet of airline tubing and one Tetra Whisper Bio-Bag Filter cartridge.