hygger External Hang-On-Back Canister Aquarium Filter,Quiet Fish Tank Filter with 3-Stage Filtration,Anti-Dry Burn Motor,Adjustable Flow,Oil Skimmer,Duckbill Nozzle,Shower Spray Bar (7W,20-40 gal)Brand: hygger Color: Black + Orange Features: FILTRATION PRINCIPLE: After power on, the built in pump generates power to form a filtered water cycle. First, dirty water is sucked in from the bottom of the water inlet pipe, and a small amount of water with an oil film enters from the oil skimmer port. The dirty water flows to the filter box, passes through three filter media, completes the filtration cycle,then clean water flows out of the outlet pipe