Abstract: An aquarium water filtration means includes intake means for aquarium water, prefilter means, and water transfer means for transferring aquarium water from the intake means to the prefilter means. Both mechanical and froth filtration of the aquarium water is carried out in the prefilter, which comprises a plurality of chambers separated by walls of different heights. The aquarium water is gravity fed into and through the prefilter, and between the various chambers of the prefilter, its flow being determined by the relative heights of the separating walls, as well as by the heights of openings in certain of the walls.