A media reactor aquarium filter incorporates a simple design and allows simple media replacement. The filter includes co-axial inner and outer tubes. The outer tube includes a mounting feature and the inner tube holds the media and is removable without disturbing the outer tube. A pump at the base of the filter pumps water into the inner tube through ports at the base of the inner tube and up through the inner tube, and thus through the media. The filtered water then flows through the top wall of the inner tube and down between the inner and outer tubes, and back into the aquarium. The inner tube is rotatable to vary the alignment of the ports to adjust the water flow rate through the filter.
