Water flow is critical on a coral reef, delivering food, oxygen, and removing waste. It stands to reason that recreating those conditions is just as important in a healthy reef aquarium. Jeremy continues his beginner's marine guide by exploring why water movement is essential for every successful reef tank.
When setting up a reef tank, most beginners focus on lighting, filtration, and choosing their first corals. While these are all essential, one of the most important aspects of a successful reef aquarium is often overlooked – water flow.
Good water movement is the lifeblood of every healthy reef tank. In the ocean, coral reefs are constantly exposed to tides, currents, waves, and swells that deliver food, remove waste, and create the dynamic conditions corals have evolved to thrive in. Recreating this natural water movement inside your aquarium using properly positioned wavemakers is essential for keeping corals healthy, preventing detritus from settling, and maintaining excellent water quality.
Whether you're keeping soft corals, LPS, or demanding SPS corals, providing the right amount of flow can make the difference between a thriving reef and one that struggles. In this beginner's guide, we'll explain why reef tank water flow is so important, how much circulation your aquarium needs, how to choose the right wavemaker, and where to position your pumps for the best results.
Want to know which tank is best for you? Read our guide to choosing the right marine aquarium.
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Why Is Reef Tank Circulation So Important?
The oceans are constantly moving, and water flow is arguably even more important to corals than light. Many deep-water corals survive with little or no light, gaining much of their nutrition by capturing zooplankton, but no coral can survive without water movement. Water movement delivers food and oxygen to corals while carrying away waste products and mucus.
Water movement on coral reefs is powerful, unpredictable, and constantly changing. Corals have evolved to thrive in these conditions, with currents pushing them in one direction before rapidly changing with tides, waves, swells, and eddies. These ever-changing currents are not only essential for the survival of a reef but also play a vital role in coral reproduction.
Most corals are broadcast spawners, relying on ocean currents to carry eggs and sperm over long distances, allowing new coral polyps to settle and establish new reefs. Reef fish also depend on water movement to bring them food and disperse their eggs and larvae.
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To recreate these natural conditions, reef aquariums need strong, varied water movement. But what equipment should we use to create this dynamic environment?
Related article: How to set up a marine fish room for breeding.
What Is A Reef Tank Wavemaker?
Reef keepers create this natural water movement using specially designed pumps called wavemakers. These pumps sit inside the aquarium, usually one at each end, creating broad water movement throughout the tank.
Unlike traditional powerheads, wavemakers use propellers, rather than impellers, to generate extremely high flow rates over a wide area. This allows corals to receive strong, turbulent water movement without being blasted by a narrow jet of water. Modern wavemakers typically produce between 2,000 and 30,000 litres per hour (440–6,600 gallons per hour).
Just like lighting, different corals have different flow requirements. Soft corals generally prefer gentle to moderate water movement, while LPS corals usually enjoy moderate, indirect flow. SPS corals, however, thrive in strong, turbulent circulation.
Most experienced reef keepers aim to turn over the entire aquarium volume around 20 times per hour for low-flow systems, 40 times per hour for mixed reefs, and as much as 100 times per hour for heavily stocked SPS aquariums.
How Much Flow Does A Reef Tank Need?
Let's do the maths. If your aquarium holds 250 litres (55 gal), you'll need at least a 5,000 LPH (1,100 GPH) wavemaker to achieve a turnover of twenty times per hour. Two 5,000 LPH pumps, or a single 10,000 LPH (2,200 GPH) pump, would increase this to around forty times turnover.
New reef tanks usually contain fewer corals, so this amount of flow may initially seem more than enough. However, as corals grow and fill the aquarium, they restrict water movement and create areas of poor circulation. Many experienced reef keepers gradually add extra wavemakers as their reefs mature to eliminate low-flow or dead spots.
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Immature reef tanks are often prone to cyanobacteria, commonly known as red slime algae. This nuisance photosynthetic bacteria can spread across rocks, sand, and even corals. Strong water movement helps prevent it from settling by reducing stagnant areas and keeping debris suspended so it can be removed by your filtration system. It's another excellent reason to provide plenty of circulation from the start.
Can A Reef Tank Have Too Much Flow?
Most experienced SPS reef keepers and coral reef divers would argue that it's almost impossible to recreate the immense force of natural reef waves. Even turnover rates of 100 times per hour don't come close to the energy experienced on a shallow reef crest during rough weather.
However, not every coral enjoys intense flow. Large, fleshy LPS corals often struggle to expand fully when exposed to constant, direct water movement.
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Related article: Carrying a torch for LPS corals.
Creating a successful mixed reef is therefore all about coral placement. High-flow SPS corals should be positioned where they receive plenty of turbulent circulation, while lower-flow corals, such as mushroom corals, are better suited to more sheltered areas around the base of the rockwork.
One advantage of buying a larger, controllable wavemaker is that you can always reduce its output. As your reef matures and corals grow, you can gradually increase the flow rather than having to replace an undersized pump later.
Where Should I Place My Wavemakers?
The ideal placement of your wavemakers depends on both the number of pumps you have and the aquascape you've created.
If you're using a single wavemaker, position it so that it creates flow along the full length of the aquarium. Ideally, place it at the opposite end of the tank from the return pump outlet to encourage water movement throughout the entire system.
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With two wavemakers, you can either position one on each side of the aquarium facing towards each other, or mount them on the rear glass facing forwards. Both arrangements help create more random, turbulent water movement than a single pump alone.
For even better circulation, try creating a gyre flow pattern. Position one wavemaker high on the right-hand side of the aquarium towards the rear glass, and the second low on the left-hand side towards the front glass. This creates a circular flow around the tank that helps keep detritus suspended, reduces dead spots, and improves overall water quality.
Avoid pointing a wavemaker directly at your rockwork, as this can create areas of excessive flow while leaving sheltered dead spots behind the rocks. If you're still designing your aquascape, keep pump placement in mind before fixing the rockwork permanently. If your aquascape is already established, you may simply need to adjust the pump positions slightly to achieve the best possible circulation.
Conclusion
Water flow is every bit as important as lighting and filtration when it comes to building a successful reef aquarium. By choosing the right wavemakers, providing sufficient turnover, and creating varied, turbulent water movement throughout the tank, you'll give your corals the conditions they need to grow, feed, and thrive.
As your reef matures, don't be afraid to adjust your pump settings or add extra circulation if your growing corals begin to restrict water movement. Get the flow right, and you'll be rewarded with healthier corals, cleaner rockwork, and a more stable reef tank for years to come.
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