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Huijukon Air Pump Double Sponge Filter for Aquarium Fish Tank Up to 55 Gallons - The Aquarium Petshop
Sponge filters provide both mechanical and biological filtration -- Works great,easy to clean (squeeze in tank water), keeps water cycled and clear. Simply install an airline into the unit and provide both aeration and filtration for your fish Aerobic bacteria colonize the sponge providing a bacterial substance to facilitate the nitrogen cycle