Lees Premium Under Gravel Filters clean your freshwater or saltwater aquarium through a biological filtering process that supports the growth of beneficial bacteria. This allows natural detoxification and maintains proper ammonia balance by circulating water flow through the gravel bed. Under Gravel Filter Circulates Water Flow Through the Gravel Bed Requires the use of an Air Pump not included Maximize Water Quality by Using a Power Filter Provides Biological Filtration Can be used in Freshwater Aquariums and Saltwater Aquariums Lees Premium Undergravel Filter has a multi level plate design made of special quality plastic which resists splitting or cracking. The larger plate sizes reduce the number of plates required. The added strength of the UGF plates makes this filter most preferred by saltwater aquarists Under Gravel Filter Dimensions 5.5 Gallon Undergravel Filter 8 Inch x 16 Inch 10 Gallon Undergravel Filter 10 Inch x 20 Inch 15 20H Gallon Undergravel Filter 12 Inch x 24 Inch 20L 29 Gallon Undergravel Filter 12 Inch x 30 Inch 40 55 Gallon Undergravel Filter 12 Inch x 48 Inch 50 60 Gallon Undergravel Filter 18 Inch x 36 Inch 70 90 Gallon Undergravel Filter 18 Inch x 48 Inch 125 135 Gallon Undergravel Filter 18 Inch x 72 Inch lates makes this filter most preferred by saltwater aquarists