Abstract: The present invention relates to aquariums or reef tanks and especially those in which living corals reside. Besides providing a pleasing visual effect, alternating currents within the aquarium are beneficial to the proper health of living corals. Pressurized water from a pump or powerhead is directed by a shuttle valve to one of two outlets. A rod is attached to a plunger through a seal. The rod moves axially by the influence of the pump or powerhead. In operation, a moving seal shuttles back and forth, alternately sealing one of a pair of valve bodies. When moved, the plunger with the attached rod is pulled in, thereby blocking flow to one valve body, while opening flow through the other valve body. By alternately moving the perspective plungers, flow of water within the aquarium tank is alternately diverted from one valve body to the other, providing the desired wave motion in the aquarium tank.