How Do Under-Gravel Aquarium Filters Work?
Under gravel filters consist of a plastic grate or “filter plate” which lies under the gravel of the tank. This plate allows water to flow freely under the gravel. Water is drawn through the gravel (which acts as a mechanical and biological filter). To move the water, you can use either power heads or air pumps. A power head will pump water out of the top of the lift tube and into the tank, and air pump will blow bubbles at the bottom of the lift tubes and the bubbles will lift water up the lift tube and into the tank. As water is moved out of the lift tube, it is replaced with water from under the filter plate, which in turn pulls water through the gravel where it is cleaned. The gravel it self provides mechanical filtration by catching large free-floating particles. The gravel, as well as the filter plate, tank bottom, and lift tubes, provide a bed for the bacteria of a biological filter. Under gravel filters primarily provide biological filtration.
