Water Flow and Movement
Generally speaking, our goal is to manage in a relatively small closed system, an environment that mimics the natural environment (a very large, open system) of the animals and plants we are keeping — think, Great Barrier Reef. Note though that wide variations appear to all “work” successfully.
On a natural reef, there is a gentle flow around the coral head every two to three seconds. Every 10 seconds there is a second much stronger surge. Lastly, tidal flow moves unidirectionaly twice a day. The flow rate is reported to be 4-19 inches per second — tough to even approximate in an aquarium.
For your aquarium:
General rule is a minimum of 10x your tank volume per hour. For high flow animals like SPS corals, consider up to 20x. Some reef keepers insist on 40-50x.
The water needs to be moving both within the display tank, and through the sump (the water treatment and filtration area). How, when, where, and how much depends somewhat on the animals.
3-5 times your display volume per hour through your sump should be sufficient for filtration purposes.
Flow and movement can be achieved from a combination of the return pump and devices (pumps, wavemakers, propellers) placed directly in the display tank.
Power heads (PH)
Propeller like devices placed in the display tank that move water.
Sump return lines
The sump return lines are often outfitted with nozzles like accelerators to provide water movement within the display tank (DT).
Simply put, an external pump(s) pulls water out and then blasts it back in.