There are two types of water movement in the tank – surge and turbulence.
Surge
Surge is a movement of water back and forward across the reef as if caused by wave action. It will push sea fans one way and then the other, almost at right angles.

Turbulence
Turbulence is more a random movement of water in all directions causing eddies and isolated disturbances. It will make soft and leather corals gyrate in all directions.
By creating medium to power surge and turbulence within the aquarium, a host of advantages will become apparent:
Carbon Dioxide (Co2)
Co2 will be dispersed far more quickly. As it is a tendency to acidify the water, causing the pH to drop, having less of this gas in the tank will eliminate one cause of pH crash.
Oxygen (O2)
O2 will be encouraged to enter the water more readily and raise the pH slightly. This is because dissolved oxygen tends to make more alkaline and higher pH results. As an additional bonus, reasonable levels of CO2 and O2 will encourage greater health and vigour in fish and invertebrates.
Unwanted Gas such as nitrogen (produced as a result of denitrification taking place on and within the rocks etc.) and ammonia are removed much more rapidly where circulation is brisk, especially at the surface water.
Uniformity of Temperature – The Constant and frequent mixing of water eradicates “hot” and “cold” spots.
“Dead” Spots are where water has a tendacy to stagnate are less likely to occur.
Animal Waste products are removed quickly and efficiently especially from sessile invertebrates. Conversely, nutrients and fresh supplies of the elements found in saltwater are brought into contact with livestock on a more frequent basis.
Detritus is prevented from accumulating, drawn swiftly into solution to be removed by the filters.
Physical stimulation of surge and turbulence benefits the health of most livestock.