Abstract: An improved filtration system for an aquarium having a water-filled habitation area with the water being aerated and circulated. The filtration system comprises a perforated platform adapted to be placed on a bottom surface of the aquarium and covered by a layer of porous material. The platform and the bottom surface define a subspace therebetween, and perforations admit water that circulates between the habitation area and the subspace. A hollow column, having an interior in fluid communication with the subspace, and carrying water circulating therethrough, extends through the platform and at its terminus discharges the circulating water back into the aquarium. A plurality of media elements, located in the column, each has a large surface area portion that is exposed to the circulating water.