Penn-Plax® ClearFree® Premium Undergravel Aquarium Filters keep your aquarium water clean & crystal clear. Available in sizes for standard aquarium tanks from 5 gallons to 55 gallons, ClearFree® Undergravel Filters are easy to assemble and come with the necessary Filt-A-Carb® cartridges to keep your water looking beautiful. The Filt-A-Carb® cartridges (included) use activated carbon to remove harmful gases, odors and discoloration, and the even filtration draws water through the entie gravel bed. High pore air diffusers increase bubble flow while the jumbo adjustables 1" lift tubes allow for acceptional filtration and can be used with powerheads. The adjustable tubes allow you to set the height to match your water level and collar caps cover the lift tubes when not in use keeping your fish safe. Base plates are slotted & sloped for greatest efficiency and the sure-fit lock design insures the lift tubes are secure. The Gravel Guard® keeps fish and gravel from getting under your filter plates so there are no worries. Simple to maintain, ClearFree® Premium Undergravel Aquarium Filters will keep your aquarium water crystal clear. Available in sizes for 5, 10, 20, 29 & 55 gallon standard aquarium tanks. Four panel 55 gallon filter covers a 11-1/2"x 46" area.