Water flow in the reef aquarium is extremely important. Water flow not only provides for vital surface gas exchange, it also brings the food to the corals and keeps the food in suspension longer so all of it can be consumed by the corals and fish as apposed to having it settling on the bottom and rotting. The proper flow will also encourage the coral polyps to open up and improves the coral feeding efficiency. Hard to keep corals like Dendronephthya hemprichi were most efficient feeding on phytoplankton with a flow rate of 6-8 inches per second (15-20 cm/s). Moderate water motions with an occasional strong burst are preferred by zoanthids. This type of flow will prevent accumulation of detritus between the polyps. If your flow is weak, sand and detritus will accumulate between the polyps and promote the growth of undesirable algae. The right type of water flow is also important to anemones as well. Not only will the right flow bring food and oxygen the right flow will change the position of the tentacles affecting the rate of photosynthesis. Anemones like Heteractis magnifica aka Ritteri anemone and Stichodactyla mertensii are found on the outer reef slopes were there is a strong surge. Anemones like Stichodactyla gigantean aka giant carpet anemone are found on the less exposed areas of the reef but still need a strong gentle flow to thrive.
Basically there are three types of water flow, surge, turbulence and laminar flow. The Surge is a back and forth water movement caused by ocean swells and wind caused waves. This surge is highly important to many reef organisms, especially to all corals and anemones. According to J. Charles Delbeek and Julian Spring, “the back and forth movement exposes more of the surface area to light, increases the feeding efficiency of polyps and greatly helps in the exchange of metabolites and gases with the water”. Turbulence is a random movement of water mostly caused by different currents clashing and moving around objects. Laminar flow occurs when a fluid flows in parallel layers, with no disruption between the layers. It is the opposite of turbulent flow. In nonscientific terms laminar flow is smooth while turbulent flow is rough. A good example of laminar flow in a reef is the tide coming out and then in several hours later. Quality Pumps like Tunze and VorTech have controllers that can simulate all three types of water flow. For more information click on VorTech Pumps.
Proper water motion also enhances you lighting. Having waves on your aquarium water surface creates glitter lines. Basically the waves act like a magnifying glass, temporally increasing and decreasing the intensity of your lights. Photosynthetic corals are uniquely adapted to take advantage of this. This glitter or shimmer is very relaxing and pleasing to the eye. It also is most pronounced with Metal Halide lighting. Click here for more info on Metal Halide or here for Metal Halide Fixtures.
Water motion is also important in aquaculture. Some corals after being fragged are stressed produce copious mucus. This mucus surrounds the coral blocking water and gas exchange thus suffocating itself. This mucus and injured tissue can also promote the growth of less than beneficial bacteria. You need a flow that is strong enough to blow away the mucus but not strong enough to blow the frag off the plug. Click on Coral Propagation for more info on fragging and aqua culture.
To improve the overall water motion in the aquarium we highly recommend the use of eductors and or a Wave Box. An eductor is a basic venture nozzle that accelerates the water from the pump. As it leaves the nozzle a low pressure area is created, drawing the surrounding water through the venture. Eductors come in many sizes from ¾” Diameter to as large as 1 ½” Diameter. We have our ¾” eductors attached to two separate Sea Swirls and powered by a 1500GPH pressure rated pump. An eductor can increase the overall water flow by up to five times under optimal circumstances. In our experience expect to see a two to three times increase in overall water motion. An added benefit of an eductor is it changes the harsh concentrated flow from a pump to a broad gentile stream which in beneficial to corals. Click her for more info on Eductors. A wave box simply allows water flow when the pump is in its off cycle. Click here for more info on Wave Box.
Surge devices are very popular with aquaculture facilities as they provide the necessary flow at a very reasonable price. There are two common surge devices used in the hobby. Carlson Surge and the Borneman Surge device. Both work very well however they both have a downside…Noise. We plan on implementing a surge device into our system this spring. The only difference is that we will have plumbed into a separate sump room and have two refuges in series. We’re looking forward to the results. In theory we should have a reliable varied surge without the bubbles or noise.