Abstract: A filter cartridge comprising a framework and a surrounding envelope of filter material. The framework is reusable and provided with a rough, granular surface texture to provide increase surface area available for the propagation of aerobic bacteria. The envelope is disposable. Thus, biological filtration of the water provided by the aerobic bacteria is not interrupted upon replacement of the filter material. A second filter medium may be disposed within the envelope. The envelope is held in place by a pair of flaps which sandwich an edge of the filter material.

Abstract: An aquarium filter for mounting externally of an aquarium tank. The filter includes an intake chamber for receiving contaminated aquarium water from the aquarium tank and a filtering chamber in flow communication with the intake chamber for filtering of the contaminated water and subsequent return of the clean water back to the aquarium tank. An impeller unit driven by a rotor magnetically coupled to a removably attached electromagnetic stator unit serves to draw the water from the aquarium tank to the intake chamber through a removable intake tube assembly. A partition wall separates the intake chamber from the filtering chamber for the water filling the intake chamber to overflow the partition wall into the filtering chamber. Upon stoppage of the impeller, the water from the intake chamber siphons back into the aquarium tank.