Most corals and other reef invertebrates need vigorous water motion simulating the action of waves and tides if they are to remain healthy and grow in a captive environment. One of the ways we create such water motion in our tanks is by the use of an Algal Turf Scrubber filter that dumps approximately one gallon of water into the back right corner of the tank every 40 seconds or so. While the primary function of this unit is to use highly efficient turf algae to remove nutrients from the water, the dumping action provides a significant secondary benefit by producing strong water surges in the tank.
More information on the design and operation of Algal Turf Scrubbers can be found at: http://inlandaquatics.com/ats.htm
Also see The Biology and Methodology of Reef Aquaria, and Technical Details of Augsburg's Marine Aquarium System.