Abstract: The present invention is directed to a filtering system and method of filtering an aqueous medium, such as water in an aquarium tank. The aquarium water is brought into contact with a filtering medium, preferably a biological filtering medium. The filtering medium purifies the aquarium water by removing impurities from the aquarium water. At a certain time, the water is rapidly removed from the filtering medium, preferably by siphoning action. The process and system provides the biological filtering medium with exposure to air necessary to sustain the life and activity of the bacteria growing on the biological medium. At the same time, the system purifies the aquarium water.