Abstract: An aquarium including a tank disposed above a housing, a screen disposed in the housing, a space formed below the screen, a conduit coupling the tank to the housing for supplying water from the tank to the housing and to the space, an outer tube vertically disposed in the housing and an inner tube disposed in the outer tube and having a lower end extended outward of the housing. The water contained in the space is forced to flow into the outer tube and to flow out of the housing via the inner tube when water is supplied into the housing and the space from the tank.