The Pro Clear Aquatic Systems Red Flex 4-in-1 Sump â 400 is a highly efficient sump system designed for saltwater or freshwater aquatic environments. Boasting four distinct filtration methods, this unit ensures only the highest quality of water for the sensitive inhabitants of your tank. The physical filtration comes from the gravitational flow through the micron filtration bags, mechanical filtration via the skimmer pump, chemical filtration when engaging the chemical media cartridge and biological filtration comes courtesy of the built in refugium compartment. The Pro Clear Aquatic Systems Red Flex 4-in-1 comes with an easily adjustable flow gate that provides complete control over the volume of water entering the refugium. Sophisticated, durable design constructed for smooth, quiet operation. Suitable for tanks up to 400 gallons.