The AquaTop Red Devil Series of Hang-on Canister Filters are compact, quiet and energy efficient. The RD-30G has a maximum flow rate of 135 GPH and adjustable valves allowing you to customize the flow rate of your particular setup. Each unit efficiently filters fresh and saltwater aquariums up to 30 gallons and comes with a multi-stage filtration system equipped with 4 filtration media trays. All the necessary filtration media is included to help keep a healthy aquarium. Fine Filter Pads and a Dense Filter Sponge collect organics into a central location for easy removal, providing excellent Mechanical Filtration, while Activated Carbon provides Chemical Filtration to keep aquarium water crystal clear and free from odor. The included Ceramic Rings help maximize Biological Filtration and offer a porous structure for beneficial bacteria to grow and help maintain safe living conditions for your aquatic creatures to thrive. For twice the amount of filtration the RD-30G is expandable with the optional RD-Pre Hang-on Filter, allowing double the filtration capacity.