One of the most important things to remember when caring for an underwater coral reef environment is the water flow. Different types of coral require different flow rates, but most people say that a turnover rate of 10 gallons per hour multiplied by the tank capacity is generally a good rate. There are always exceptions to every rule, though, which is true when it comes to coral.
Some types of coral, such as the Mushroom variety, do not require much water flow because they usually live in crevices near the base of the underwater coral reef. Other types of live coral, such as Acropora and Montipora, do well under more turbulent conditions with 30 to 40 times more flow, because they are used to breaking waves in shallow water near the tip of the coral environment. The direction that the water pumps into the aquarium has a large effect on flow speeds, so hobbyists can greatly control this aspect of the marine environment.
One of the most popular ways to control flow for an underwater coral reef tank is by using multiple powerheads, which are just small submersible water pumps. Live coral owners can randomly turn the pumps on and off with a wave timer, which creates different flow in the coral tank. Water flow is important to bring food to all types of corals, since they don't fully rely on photosynthesis for food. Water flow also helps to reduce the risk of thermal shock and damage, by decreasing the coral's surface temperature. It is very important for the success of these marine environments.
