The Pro Clear Aquatic Systems Red Flex Reef Sump â 400 is a highly efficient sump system designed for saltwater environments. Water from your aquarium flows through two separate overflow ports, into heavy-duty bubble diffusers and then through a 4 inch, 200 micron filter sock to ensure that any harmful particulate matter is removed. In case of overflow, the unit features an overflow panel so that the water can move back into the sump. In addition, the level of water leaving the refugium chamber can be quickly and easily adjusted between 6 and 9 inches depending on the needs of your set up. Sophisticated acrylic construction also provides dosing, probe and wire holders which are conveniently organized by the built in fastener. Suitable for tanks up to 400 gallons.