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.

Closed Loop Circulation – What’s That Then

After water quality and then lighting water circulation, in my opinion comes next.

Not just any water circulation though – you can’t just chuck powerheads left right and centre into the aquarium and turn it into a washing machine – you have to create the right water flow.

The water flow which you need to create depends upon the livestock you keep in the aquarium. If you are a fish only aquarist then the water circulation requirements are minimal. Corals, however are more demanding in water circulation for various reasons.

Years ago the only option which was available to saltwater aquarists was the powerhead and to be honest we had to be creative as to the ways we positioned these powerheads to achieve optimum results.

Nowadays as both manufacturers and aquarists have learnt more about the requirements of the animals we keep there are more options available to us.

There is one option which I believe stands out above the crowd though and that is one which is called closed loop.

Closed loop circulation is where the device which creates the waterflow is housed external to the aquarium, quite often beneath the aquarium, however it can be placed anywhere. Rigid or flexible tubing is connected to the device which connected to both the inlet and outlet of the device which both go to the aquarium.

A lot of aquarists who use closed loop circulation opt to drill the aquarium and use bulkhead connectors and taps to connect the external device to the aquarium, however you do not need to do this if you don’t want to – you can go up and over the edge of the aquarium if that is easier for you.

Basically what you are doing is allowing water to be pulled from the aquarium to the external device, we will use a external water pump for this example. This pump then pushes the water along the output back into the aquarium and whilst doing this pulls more water behind it.

Now here is the good thing. In a closed loop circulation system there is no air in the pipes which means that there is no head height plus as the pump is external to the aquarium there is no heat transfer from the pump to the aquarium water.

You can setup as many closed loop as you want however each one will require it’s own dedicated pump. A huge benefit of this is that with clever plumbing you can take water from the aquarium from exactly where you want it to be taken plus you can return it to an area in the tank where you want it to be returned to.

One thing I must point out though is that if you do decide to opt for a closed loop system then I would recommend that you install close off taps to both the inlet and outlet areas of the plumbing. Doing this will allow you to remove the pump it either it requires maintenance or replacement.

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Water flow in the seawater aquarium

Whether the aquarist owns a salt water fish only or [tag-tec]reef aquarium[/tag-tec], water movement is of very great importance.

Seawater quality is measured by test kits, such as Ph, alkalinity, nitrate etc. It could be argued that another part of seawater quality is its movement. Sluggish movement, or movement of the incorrect type, can have very detrimental consequences. [Read more]