Quiet, efficient and reliable Aqua Clear 20 pumps 100 gph. Recommended for aquariums up to 20 gallons. Aqua Clear stands alone as the only aquarium power filter that offers the integrated filtration of the CycleGuard Insert System. Aqua Clear combines the largest volume of efficient filter media in individual inserts with the powerful water flows from the free floating impeller. Alternate replacement of the CycleGuard inserts ensures continuous biological removal of organic toxins can be achieved. The waterfall style output from the Aqua Clear filter agitates the surface of the water while creating beneficial currents throughout the entire volume of the aquarium. Both the surface agitation and the rotational currents bring more water molecules to the surface, in physical contact with the atmosphere, enabling them to release carbon dioxide and replenish oxygen more efficiently. In addition, the constantly moving water currents do not allow dead spots to occur in the aquarium, eliminating the possibility of thermal layering. Water input per hour is regulated by adjusting the patented flow adjustment mechanism, tailoring the flow rate to the aquarium's requirements. When the flow adjustment reduces input, the water returned to the aquarium is still equal to input, but the top grid in the filter basket circulates purified water back into the motor chamber so that the pump filters 100 gallons per hour even when adjusted to siphon less. Water may be filtered more than once without reducing the actual flow rate of the pump unit. The Aqua Clear 20 actively draws dirty aquarium water through the integrated siphon/strainer assembly into the pump impeller chamber. The flow diverter directs the powerful water current from the impeller chamber under the filter basket. The water is forced to move through the provided filter media and then returned purified to the aquarium. Aqua Clear Power Filters are designed to fully exploit the benefits of removing aquarium wastes both mechani