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 BedRequires the use of an Air Pump - not includedMaximize Water Quality by Using a Power FilterProvides Biological FiltrationCan be used in Freshwater Aquariums and Saltwater AquariumsLees 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 aquaristsUnder Gravel Filter Dimensions: 5. 5 Gallon Undergravel Filter: 8" x 16" 10 Gallon Undergravel Filter: 10" x 20" 15 / 20H Gallon Undergravel Filter: 12" x 24" 20L / 29 Gallon Undergravel Filter: 12" x 30" 40 / 55 Gallon Undergravel Filter: 12" x 48" 50 / 60 Gallon Undergravel Filter: 18" x 36" 70 / 90 Gallon Undergravel Filter: 18" x 48" 125 / 135 Gallon Undergravel Filter: 18" x 72" lates makes this filter most preferred by saltwater aquarists