Good water flow is essential in keeping a healthy and attractive reef aquarium. In fact it is only second to having the correct lighting for the growth and health of corals. In this article I will discuss types of current, reason for needing good flow, and my preferred method for creating flow in the reef aquarium.
There are no right and wrong ways in creating good water flow. One way may work for one person and not for another and there may be multiple reasons for each but the only right way is the way Mother Nature does it. We can only do our best to copy it and let the life in our reef aquarium show us if we did it right.
Corals make use of currents to bring food, oxygen, and nutrients. Water currents also carry away their waste products. SPS corals in particular depend on strong water currents for their needs and will struggle without good current if not die.
Good water currents will also keep detritus from building up in the aquarium which will create other problems like algae blooms or cyno bacteria. Good flow also feeds the bacteria in the substrate and live rock in our aquariums. It is this bacteria that breaks down ammonia, nitrite, and nitrates in the reef tank.
Laminar: Laminar flow is straight unidirectional flow. This could be created by a single power head flowing only one direction all the time.
Surge: Surge is a large volume of water going in one direction then a rest and then another surge. The idea of a surge is to try and mimic a wave action by the current going one way and then back.
Turbulence: Turbulence is the random flow of water in multiple directions.
My preferred method for setting up a reef tank for good flow is to place the live rock in the middle of the aquarium like an island. I then use power heads and the main pump to create a swirl around the island. Depending on the tank and the types of coral, I may put some live rock or coral directly in this swirling flow. Yes this is a strong laminar flow but most of the reef life will be between the two opposing flows that go down the sides of the aquarium and not into each other. Using this method I have been successful in keeping LPS, SPS and softies all in the same reef aquarium. Below is a simple diagram showing placement of live rock and power heads.
Flow into the aquarium by main pump and power head
<<<<<<<<<- Flow XX
X Flow à>>>>>>>>>>>
This is one of many methods aquarist use to get good current in the aquarium. A couple pros to this method are that it is not complicated and does not involve a lot of expensive equipment. One con is when using strong power heads, the flow hits the opposite side of the aquarium and some of the flow goes down, under, and blows out the substrate. The cure for this is to use a heavier more course substrate just on the ends of aquarium at the corners.