Penn-Plax Undergravel Aquarium Filter for 40-55 Gallon Tanks – Four 11.25” X 11.

Penn-Plax Undergravel Aquarium Filter for 40-55 Gallon Tanks – Four 11.25” X 11.25” Plates – under Gravel System for Clear, Clean Water – Safe for Freshwater and Saltwater Tanks (CFU55). ALSO AERATES YOUR TANK: Since the Clear-Free Premium Under Gravel Filter is air driven through the use of Air Stones and an Air Pump (not included), it also aerates your tank.

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