A standalone aquarium filter with a filter cage having a hinged or detachable top cover and a filter bag. The filter bag is adapted to be filled with a filtering medium. The filter cage has sides with openings sized to allow water to flow substantially transversely through the at least one filter cage and through the at least one filter bag. The filter cage is adapted to stand alone on the bottom of an aquarium tank while the filled filter bag remains substantially vertical within the at least one filter cage. A bottom portion of the filter cage further includes a ballast to stabilize the position of the at least one filter cage. The plastic material is selected to be strong enough to prevent most aquarium fish from accessing the filter media bag and scattering filter media throughout the tank.
