There are many variables to consider in creating an aquarium environment, whether a simple fish-only tank, an aquarium approximating river conditions, or a marine reef aquarium. Filtration, heating, lighting, and tank size and configuration are all issues that must be addressed. One often overlooked variable, however, is current. Any natural underwater environment is characterized by nearly constant water movement, which fish, plants, and other aquatic life have naturally adapted to. Without providing a water current in your aquarium, your aquatic environment will not be authentic, and you will inhibit the healthy growth of your aquatic life.

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A water current is particularly important for reef aquariums. Currents circulate and bring nutrients to corals, clams, and other invertebrates that are stationary. Currents also clean coral by removing waste produce and sediment; if debris is allowed to accumulate on coral, algae may grow uninhibited. Also, currents encourage your fish to swim, helping them develop muscle tissue and burn off excess fat.

Water movement in your aquarium also supplements gas exchange. Various gasses naturally form and accumulate in aquarium water; carbon dioxide is produced by fish respiration, for instance, and gasses such as nitrogen, sulfur, and methane are produced by bacteria that metabolize waste products. Water currents transport these gasses from stagnant areas to water columns, where they are released into the atmosphere. Active currents constantly move water from one level in your aquarium to another, allowing oxygen-poor water near the bottom of your tank to come into contact with oxygen-rich water closer to the surface. This overall movement reduces the concentration of harmful gasses and your tank, and increases levels of oxygen.

One other benefit of water movement is that active currents in your tank efficiently transport waste material to your tank’s filter, whether you have a biological, chemical, or mechanical filter, or some combination thereof. Waste material and debris that would otherwise hang suspended in your tank, or settle into hard-to-reach areas, are instead swept up by currents and eventually disposed of by your filter. And, because active currents enrich the oxygen levels in your tank, any biological filtration device that you have installed will be aided. This supplemental filtration is particularly important for reef tanks.

There are three primary kinds of movement that you can create in your aquarium. Laminar flow is a steady, unidirectional flow, usually created by a mechanical device called a “powerhead” that is positioned in a designated area in your tank. Surge is unidirectional like laminar flow, but is not steady; surge is an alternating current of strong forward flow followed by a weaker back flow. Surge closely approximates what you may see if you are snorkeling in a marine environment, as schools of fish move forward in tandem, then halt and sweep backward as a single unit. Finally, turbulence is the random flow of water in multiple directions. Turbulence is the most natural kind of water movement, and the most difficult to replicate in an aquarium environment.

There are several devices that you can purchase that create currents in your aquarium. Most common are powerheads; these inexpensive devices produce only laminar currents, but you can often create multidirectional currents with powerheads by fitting them with PVC piping, or by positioning two or more powerheads at different locations in your tank. Powerheads are ideal for freshwater tanks recreating a river environment, encouraging river fish to stay strong and healthy. If your tank is stocked with stationary invertebrates, do not aim a powerhead directly at the invertebrate, as the current may be too intense. However, you can aim the powerhead at certain areas where debris may build up.

An oscillating powerhead rotates within the aquarium, directing water in various directions. Installing several oscillating powerheads can recreate the turbulence required by reef ecosystems. A “wavemaker” is another device that generates turbulence by emulating the alternating strong currents and weak currents that characterize most freshwater and marine environments. A wavemaker is an electronic timing device that connects with several submerged powerheads, turning the powerheads on and off at predetermined intervals. Wavemakers can be programmed, for instance to produce slower currents at night or during feeding times.

A water flow diverter is yet another device that mixes up currents in your tank. These diverters are installed on your filter’s return, directing the filter outflow in different directions. You can connect diverters to each other, creating a multidirectional outflow. Water flow diverters are effective in creating turbulence near the surface of your aquarium, thus facilitating oxygen exchange.

Be sure that your currents are not too strong; pay close attention once you have established a pattern of currents, and observe how your fish and particularly invertebrate life responds. Aquatic life is adaptable, but coral will tend to grow around an area where currents are too strong. Also, pay attention to any salt spray, or bubbling and agitation, on the water surface. A fine layer of salt may eventually settle around your lighting fixtures, or into your heating or other devices, damaging these fixtures. If you notice excessive surface spray or bubbling, you may need to reposition your current-creating devices.