Undergravel filter system easily creates a biological filter which breaks down toxic waste and ammonia into less toxic nitrates. Colonies of bacteria, present on the surfaces of your aquarium, thrive on a constant supply of oxygen and media (gravel) with large amounts of surface area. Biological filtration is the process of breaking down toxic waste material into less toxic nitrates by beneficial bacteria. 2 filter plate system / 15.5'' x 7.5'' 

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