Why do we need water movement?
• Provides aeration by distributing oxygen.
• To imitate the natural ecosystem.
• Distributes heat.
• Many coral depend on water movement to stop the debris from settling on them.
• To carry away the metabolic waste of corals.
• To bring food to the corals.
• Even for the breeding of corals.

What is the best way to achieve water movement?
• The most common way to create water movement is with power heads.
• Most filters create water movement as water is returned to the tank.
• The best way to create realistic movement in the tank is using a wave maker.
• The next best way is to have a set of internal powerheads in the tank set on timers to come on and off at various times to create counter currents so the flow is less consistent. It is good to hide the powerheads with rocks so it is out of the direct line of vision as long as the flow is not restricted.
• Air-stones create water movement.
• The idea with water flow is not normally to blast it at the coral but to aim it on an angle to the front glass so the water fans out and creates a good flow.

How much water movement should I have?
• This depends on what type of ecosystem you are trying to create and which animals you are trying to keep.
• The general reef tank should have its total water volume turned over 6-10 times an hour by various pumps and power-heads. Be careful if you add several submersible pumps to the tank because the temperature may mount to unacceptable levels.
• For a fish only tank a turn over of 3 to 5 times an hour is fine.
• Most pumps lose about 25% of their output with the head height from the bottom of the sump to the top of the tank.

by Paul Talbot