Aquatop Aquatic Supplies' Red Devil Series of Hang-on Back Canister Filters offer a compact, quiet and energy-efficient method of filtering aquariums up to 30 gallons, the company reports. The series includes two models, the RD-30G and RD-Pre, which can be used separately or combined to expand filtration capacity, the manufacturer states. Other features include a maximum flow rate of 135 gal. per hour, as well as adjustable valves that allow custom flow rates. Each unit efficiently filters fresh- and saltwater aquariums and comes with a multi-stage filtration system equipped with four filtration media trays, the company adds.