White PVC Spring Check Valves, Slip Ends (SLIP) Low Head water circulation and nutrient decomposition Component:250 Watt Power Supply water circulation and nutrient decomposition Nexus Model: Water Volume Inside Filter Amount of K1 Micro Media included Amount of K+ Media included Maximum K1 Capacity Nexus220 135 US Gallons 18 liters 50 liters 150 liters Nexus320 222 US Gallons 20 liters 100 liters 300 liters EasyPod (for comparison) 21 US Gallons 18 liters N A 18 liters The check valve will prevent water in the filter from back flowing into the skimmer when the pump is switched off and keep water in bogs when the pump is turned off and other purposes Check valves are also essential when an external pump is being used