Abstract: A water filtration system for both fresh and salt water aquariums. The filter system housing is situated above the aquarium and consequently the aquarium water level thereby allowing gravity and not an integral system pump to return water to the aquarium after undergoing the filtration process. The water flow return rate to the aquarium is always matched exactly to the rate at which water is pumped into the filter system housing by a separate pump which is not a part of this invention. As a direct result of this, complicated valving and synchronization of pumps is not required. Gravity moves the water after intake over a distribution plate assembly and drop it over the entire surface of the biological filter material without the need for moving parts which may fail or wear out during continuous operation. Both mechanical and biological filtration occurs before the water is returned by gravity to the aquarium.