Seawater Flow, It Matters

Corals have definite preferences for seawater flow. Some, such as many hard corals, prefer high flow and others, including many soft corals, prefer a lower flow. The general guideline for seawater flow with a soft coral display is 10 times the net seawater gallonage per hour, and for SPS corals 20 times or more.

There are different types of flow and basically the one type that should not be striking corals is laminar, or flow moving in a straight line. The type of flow required is turbulent, another way of describing it is chaotic. This flow brings food to the corals and helps remove waste.

I run a soft coral aquarium, it has been running for just over eight years now. I prefer soft corals as though they aren’t quite so ‘reefy’ they move in the flow and have some lovely pastel colours. In the top area of the aquarium the current is quite strong but lower down it is considerably less.

The display includes ‘mushroom’ corals, I believe them to be Ricordea species (though I’m ready to be corrected!). They prefer a lower seawater flow so that they can expand fully. The photo above shows these, though they are the ones that have colonised an area that is in higher flow seawater. They measure around 3 inches diameter (circa 7.5cm) and are clearly being effected by the flow – their edges ripple and lift. Therefore the mushrooms have minimized the effect the flow has on them by keeping their size down.

The photo above shows one of the original mushrooms that has been placed in a low flow area. This time there isn’t a problem with seawater flow, the coral has expanded to a considerbly larger diameter, about 7 inches (circa 18cm). Though the coral edges and surface do move a little it is not particularly significant. The coral is also free to take up different postures, sometimes with an undulated surface and sometimes with an upturned edge. This wouldn’t be possible with stronger flow.

So to get the best display from a coral it needs to be in the area it prefers and has adapted to in its natural habitat. All that is needed is a little research on seawater flow and lighting needs.

  1. Good and in depth article but full of useful information

  2. I have more of a question then a comment. l have had a reef aquarium for nearly six years when I had to break it down for about six months. I have since rebuilt it and all the inhabitants are new. Sand, fish, live rock, ect. In the last 4 months every inverabrate has died. I am baffled. the coral are fine, thriving actually. I have preformed every test under the sun. Copper 0 ppm, nitrates 0ppm. every element is within a healthly range. HELP ME! I love this tank.

  3. Hello Jamie.
    Now then, you’ve really made me scratch my head! Usually there is a hint or clue as to what’s causing the problem, but not so easy here.
    I don’t know the type of corals (‘soft’ or ‘hard’) you keep but that is what has hit first, that is they are all thriving. To thrive they must have good conditions and so they physically confirm your tests – everything is ok. All the readings you have are good, you’ve even tested for copper. Of course, the corals would react badly to copper etc. Seawater, including movement, and lighting must be adequate/good.
    This leaves me to look at the specific mention – all the inverts have died over 4 months, and I also note that you have used new live rock. The rock (if it is your main biological filter) is clearly operating properly. I just wonder if you have inadvertently imported with the rock, or with later additions, a ‘nasty’ that has damaged or killed the inverts.
    As your parameters are fine and your corals thriving, perhaps the best would be to obtain one invert and properly introduce it to your aquarium. Then observe, is anything to be seen or does any problem appear with the invert? There has got to be a clue somewhere down the line! Is there an adequate food source?Damage could be caused by something very small or larger. Invertebrates rule the world by number, 97% of life is invertebrate. Not all of them are friendly. Are the fish ‘invert friendly’? No doubt they are, looking at your experience.
    I’m sad that I cannot offer a specific….but as said there has to be a clue. We’re back I think to the marine aquarist’s rule….observation and patience.
    If you do find a specific I’d love to know.

  4. Beautiful pics, I love corals they are lovely to look at. Thanks for the valuable info.

  5. Thanks a lot for this well written article.

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