Hagen model aquarium powerhead

Why water movement is important in a saltwater aquarium

Maintaining high quality saltwater is arguably the most important thing you can do for your reef aquarium. But I bet if I asked you what the most important water parameters, you would list things like temperature, pH and nutrient/contaminant levels, right? Well one important water parameter is often ignored, neglected, or otherwise taken for granted–and that parameter is water movement.

aquarium powerhead costsIf you are like me–you probably thought about water movement when you first set up your tank–and haven’t really thought much about it since then. But water movement is a critically important aspect of water quality, and whether you are planning to set up a new saltwater aquarium or if you have an existing tank, it is worth taking a closer look at the water movement in your tank.

The type, direction and velocity of water movement in in a saltwater aquarium is one of the most important environmental variables to the long-term health of the inhabitants in your tank. It’s as important as temperature, pH and chemical composition.

Proper water movement does the following:

  1. Facilitates gas-exchange
  2. Food delivery: water movement transports food to sessile invertebrates as well as creatures hiding in burrows, tunnels or within rockwork
  3. Waste management: Keeps detritus or other waste suspended in the water (to be later removed in your filter)
  4. Keeps dead zones from developing in your tank

1. Gas Exchange

aquarium powerhead costsOK, so I got this one wrong on the Saltwater Aquarium Blog exam–apparently gas exchange is not something that happens when you and a friend eat a greasy cheeseburger in a car with the windows rolled up (I’m kidding…you know that…right?). On a more serious note–gas exchange is a fancy term that just refers to the movement of gases through the water. Fish and coral breathe in oxygen and breathe out carbon dioxide, just like land-bound animals. Water movement helps with gas exchange by taking the carbon dioxide away and replacing it with the water equivalent of ‘fresh air’. Water movement along the surface of the water also promotes gas exchange for the whole aquarium. Now…go have a cheeseburger with a friend in a car with the windows up and test my other hypothesis…let me know what you find out.

2. Food Transportation

Most corals are the ultimate couch potatoes–they don’t move very much at all–and so they depend on water movement to literally bring them their meals. The best water movement will be in the goldie locks zone for your corals–not-too-fast and not-too-slow. Also, many fish burrow, hide or perch–waiting for the right-sized food morsel to drift by at the right rate–so this feeds them and supports more natural behaviors for them too.

3. Waste management

Water movement is also in the waste management business. At work, we say that ‘stuff’ rolls downhill. Well, in your saltwater aquarium, waste falls to the bottom–but with strong water movement–waste and detritus can stay suspended long enough to get sent to and cleaned up by your filter.

4. Keeps Dead Zones Away

If a tank doesn’t have enough water movement, there will be pockets where the water current is so low that bad things start to happen. Those dead zones are footholds problem algae and other things start.

But not all water movement provides the same value

The water movement around most reefs is usually characterized as turbulent–which basically means it is a chaotic, non-predictable flow pattern. Water flow on natural coral reefs comes from underwater currents, wind, wave-action and tides. All of these forces converge on the water and create the vibrant, life-sustaining water movement of the coral reef.

The water movement created by most pumps or powerheads by comparison is called laminar flow. You can think if laminar flow as being water movement in a straight-line. Most aquarium pumps or powerheads suck water in on one side and spit it out the other side.

You may be wondering then, how you are supposed to create a turbulent flow when your equipment (with its laminar flow) is conspiring against you? Well don’t despair–you do have options.

Hagen model aquarium powerheadOne of the easiest things you can do is simply point two or more of the pumps in a way that the water movement they each create crashes into the other or into an obstruction like a piece of live rock. You could also set your pumps up on a timer, designed to turn pumps on and off in a sequence to create a more pulsatile (and less regular) flow. Finally, you could add a wave-maker or surge device to complement the water flow created by your pumps or powerheads.

Changes in your water movement can hurt the animals in your saltwater aquarium. A clogged intake sponge or powerhead jammed by a snail shell can alter the water flow in your tank enough to cause serious stress to the corals and other invertebrates in your tank. I had a powerhead detach from the aquarium wall and the redirected flow destroyed a prized LPS coral.

The fish and corals in your aquarium acclimate to the flow of water in your tank–just as they do with every other water parameter–and even changes from a less desirable water flow pattern to a long-term more desirable water movement pattern may cause stress to the individual organisms in the short term. As such, you should take care and acclimate the affected organisms as delicately as possible to any changes you make to the water movement in your tank.

Finally, make sure you check out the efficiency of the pumps you are using to create the water movement in your saltwater aquarium. The costs to run these powerheads can vary dramatically based on what model pumps you are using.

Written by Albert B. Ulrich III–author of The Reef Aquarium Series of books:  The New Saltwater Aquarium Guide, How to Frag Corals, 107 Tips for the Marine Reef Aquarium

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