Experience the power of 3-D filter design! When it comes to the latest in filtration technology, it doesn't get any better than AQUATOP's 3D-HOB Power Filter. This compact, powerful, yet quiet hang-on back filter takes a three-dimensional approach to zero bypass. Aquarium water is pre-filtered before passing through the pump and entering the filter cartridge. Water enters the enclosed filter cartridge filled with activated carbon and can only exit one way, past the Activated Carbon and through the filter cartridge! This ingenious design filters every single drop of water, making the 3D!HOB one of the most efficient aquarium filters on the market.