The AquaTop Red Devil Series of Hang-on Canister Filters are compact and versatile. The RD-PRE allows for a maximum flow rate of 135 GPH and offers a customizable flow rate for your particular setup. Each RD-PRE is compatible with the RD-30G and universally attaches to Powerheads and most Internal Filters for power and water flow. The RD-PRE provides superior filtration for fresh and saltwater aquariums up to 30 gallons. The RD-PRE includes a multi-stage filtration system equipped with 4 filtration media trays for superior performance. Each Unit Includes Filtration Media Fine Filter Pads & a Dense Filter Sponge provide excellent Mechanical Filtration Activated Carbon for Chemical Filtration keeps aquarium water crystal clear and free from odor 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.