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.

Are Rotating Powerheads Any Good?

There are several important factors that should be present if a marine aquarium is to be a success. In both fish only and reef aquariums seawater movement is one of them.

One reason for the importance of movement is oxygen intake, if it is adequate the seawater will constantly reach air/water interfaces, in particular the display aquarium surface, where gas exchange can take place. Another reason is that it assists corals obtain food and rid themselves of mucus.

There are several ways of providing adequate movement, some advanced and some ‘basic’. It is likely that many (most?) aquarists use ‘basic’ equipment, namely powerheads. These devices are available in more than one type, though they are all basically an electric motor made seawater safe by encapsulating it in resin, the motor drives an impellor, and there is a seawater intake and outlet. The powerheads could be narrow outlet or wide (‘soft’) outlet types. The wide outlet ones are able to move large quantities of seawater but because they push out the seawater on a wide front the impact is soft and not harmful to corals, particularly if there are two in opposition or they are timed. Narrow outlet powerheads pump a much thinner stream of seawater which is very linear and can damage fairly close corals because of the force.

Random and chaotic seawater movement is the aim and this is often obtained by placing powerheads in opposition to each other and also ‘bouncing’ the outlets off the glass. This should result in the desired seawater flow once a bit of trial and error with powerhead positioning has been completed.

With the narrow outlet powerheads there is a further option and this is to use the generated flow of the seawater to drive a mobile directional outlet. This type of outlet can be bought as an ‘add on’ or alternatively a powerhead obtained which has the required outlet fitted. What happens is that the flow of the seawater from the powerhead causes the outlet to swivel from side to side in an arc. The movement of the outlet is not particularly fast and when the end of the arc is reached the direction is reversed. Another method is an outlet that spins, the seawater acting something like jet propulsion driving it round.

This idea has merits. The seawater flow is automatically being re-directed continuously which is good and in itself is going to create varying currents in the aquarium. If there are two powerheads present, for example, and each has a rotation ability then continuously varying seawater flow will be generated at each end of the aquarium. In addition, from time to time the outlets will come into direct opposition to each other and create more random currents.

Of course there have to be disadvantages! First of all, the rotation is driven by the outlet from the powerhead which detracts from the strength of the flow, though this could be compensated for by the powerhead strength itself. The rotation mechanism is submerged in seawater and there is the possibility (probability?) that the rotation will slow down or cease because of calcareous build up. Also, the seawater from the outlet is still linear even though it is rotating, though it would hit a coral that is in the way X number of times per minute rather than continuously. Standard powerheads require their outlet strength checking from time to time and in addition the rotating powerhead needs checking to ensure the rotation mechanism is operating correctly, meaning there is a small addition to routine maintenance checks.

Rotating powerheads are a useful idea and I have nothing against them. However, and this is purely personal, I prefer standard powerheads that have been correctly sized and placed. Better in a suitable aquarium would be wide or ‘soft’ outlet powerheads in opposition, or timed.

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Re-iterating The Importance Of Aquarium Water Movement

Seawater that is not moving or sluggish could be close to ‘dead’. In that condition it is not going to carry out the important functions that are necessary.

I remember once reading in a marine hobby book that the aquarist needn’t worry too much about fish and seawater movement, the fish swimming about would create enough movement. Er, sorry, but wrong! Admittedly the book was read many, many years ago and the author would be correct in one respect – as the fish swam along the seawater would move past them. This was written in the days well before corals had made an appearance, but nevertheless we now know better, a fish only aquarium would not be healthy without sufficient seawater movement.

So why is seawater movement so important? The movement supports important functions without which there would be problems.

The seawater needs to move fairly vigorously, not a maelstrom but significant. The movement should not be linear but random and chaotic.

In a fish only system the guideline is around 10 times the net gallonage of the display aquarium. Any gallonage in a sump is ignored. The first thing achieved is that oxygen in the seawater is plentiful. Oxygen is taken in at air/water interfaces, and the biggest one of these is the seawater surface in the display aquarium. Seawater is constantly moving to the surface and away again hopefully saturated with oxygen, which is then carried to all parts of the aquarium system including the sump if used. It can be seen how important sufficient oxygen intake is when it is considered that seawater in a marine aquarium with a high oxygen content is often between 6 and 8 ppm (parts per million). Not exactly a high ratio! In a heavily stocked fish only aquarium the demand for oxygen by the fish is high. Obviously a drop in the oxygen supply would cause fairly rapid symptoms such as fish close to the seawater surface where the oxygen content would be higher. The second advantage to fish is that the seawater movement prevents an ‘envelope’ of static seawater from developing around the fish, which, as I understand it, could interfere with the fish’s osmotic requirements. The movement, on a much more secondary level, makes food move about attracting the fish and inviting them to chase it down.

In a soft coral reef aquarium, fish or no fish, the guideline for seawater movement is the same as in the fish only system which is about 10 times the gallonage of the display aquarium per hour. The seawater is oxygenated in the same way, and the movement brings this oxygen to all parts of the system and around the corals. Branched soft corals can be seen responding to the movement as a field of corn does to wind, and the corals are likely to extend their polyps further than in a system with poor circulation. Some corals would not exhibit their polyps at all. The seawater movement helps the corals clear mucus and debris from their surfaces and also brings food within reach.

Generally SPS (soft coral stony) hard corals require more movement than the soft variety. The guideline is around 20 times the net gallonage of the display aquarium. This seawater movement gives the same advantages to the hard corals as it does to the soft types – it causes better polyp extension, clears the surface of debris and mucus, and brings food. The reason more vigorous movement is required is because of the area the corals inhabit on the reef.

When an aquarist is considering purchasing a coral, consideration should be given to the area on the wild reef the coral would normally inhabit. This will permit better placing of the coral on the captive reef in relation to light and seawater movement. It is quite possible for an aquarist with a hard coral reef system where seawater movement is around 20+ times per hour to keep soft corals (subject to compatibility) – the guidelines are not that rigorous. The seawater movement lower down is often more subdued and suitable for soft corals.

When all is considered, there aren’t that many demands that have to be met for a healthy marine aquarium. Top of the list is seawater quality. This includes oxygen content which means sufficient and appropriate seawater movement is required.

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Closed Loop Circulation – How Hard Is It To Install

Creating good water movement in the aquarium is required in order for the [tag-self]aquarium filtration[/tag-self] (if live rock is used) to be both efficient and effective, for the correct oxygenation to occur and for the transport of both food and waste around the aquarium.

A lot of aquarists simply utilise a few (or more) powerheads and strategically place these around the aquarium hoping to create the required water movement. In a lot of cases this works and the water movement created is excellent. Other aquarists also decide to utilise spraybars under or behind the rockwork as well as near to the water surface.

With enough patience mixed with a bit of ingenuity excellent water movement can be achieved.

There is another way though and in my opinion it is a better way.

Closed Loop Circulation.

There is a lot of confusion when it comes to closed loop circulation and to be honest once you understand how it works it really is not that hard to implement.

Closed loop circulation works by water being taken from the aquarium down to an external water pump, this water pump then pushes the water back up to the aquarium where the water circulation is created.

The above is a very high overview as to how closed loop circulation works so I shall try and go into a litle more detail.

The water inlet is submerged in the water. This can either be via overflow pipework which goes up and over the aquarium lip and down to the water pump or it can be via a hole drilled in either the side or base of the aquarium.

This pipework is then attached to the water pump. In a lot of cases it is impossible to directly attach the rigid pipework to the pump so the rigid pipe needs to be attached to flexible tube which is then attached to the pump. Actually I would not recommend attaching rigid pipe to the water pump due to possible vibrations created by the water pump. The rigid pipework can be attached to the flexible pipework by heating up the flexible pipe and then gently stretching it over the flexible pipework.

The outlet of the water pump needs to be attached in the same manner.

The pipework is then returned to the aquarium again either by going up and over the aquarium lip or via drilled holes in the aquarium base.

As with the inlet the outlet needs to be underwater.

The outlet is the interesting part. You can have one outlet or you can have two, three possiblly more. The number of outlets depends upon the power of the pump and how creative you are with your plumbing. For example you could have a single closed loop and from that closed loop have 3 outlets at the bottom front of the aquarium pointing up the reef face (one on the front left hand corner, one in the center front and one in the front right hand corner). All of this from one pump!

Of course you do not need to have just one closed loop, you can have as many or as few as you want or need.

Lets pretend for example you have three separate closed loops. One of these is pushing water up the reef face from the front (closed loop 1(very good for oxygenation)), another is pushing water through the rockwork from the rear (closed loop 2) and the thrid is near to the water surface at the top to create additional water movement (closed loop 3). You would get a huge amount of water movement from those loops. Now imagine what you could do with a bit of creativity. You can get the exact [tag-self]water circulation[/tag-self] that you want and your aquarium needs.

Lets step back a little. Why do both the outlet and inlet need to be under water?

In a closed loop system there is no oxygen whatsoever in the pipework. There is just water. For this reason there is no head loss on the water pump, therefore you will get all the power out of your pump without losing any power at all. The reason for this is that the water does not have to fight against gravity and is being pushed upwards by the water pump. At the same time water coming dowm from the inlet is being pulled along by the water in front of it which in turn is also strangely enough pusing the water along in front of it.

So how do you remove all of the oxygen from the pipework?

It is important to note at this point that it does not matter if the outlet is of drilled hole type or the up and over the lip type. The important part is the inlet.

In a closed loop where the inlet is a drilled hole in the aquarium then this is very easy as the water will flow down through the hole down to the pump. At this point you simply turn the pump on and all the remaining oxygen is pushed out of the loop – job done.

In a closed loop where the inlet goes up and over the aquarium lip you need to be able to lift the water up into the pipe until it overflows down to the pump.

This is actually very easy to do and there are a couple of ways to do this.

The first way is to simply push some airline into the inlet right to the upper bend and then suck all the air out. Once you get a mouth full of salt water then you are done. Cover the airline so that air does not get sucked back in and start the water pump. The water pump will push any remaining air out of the loop.

The second way is to drill a small hole in the top of the pipe (right where it overflows over the top of the lip). In the hole insert a piece of airline and a gang tap. Then simply suck on the pipe until you get (or nearly) a mouth full of saltwater. At this point close the tap and start the pump. As before the water pump will push out any remaining air.

On a closed loop system I would reccomend that you install shut off valves into the pipework onto both sides of the water pump. This way you will be able to close the taps and remove the water pump for maintenance or replacement if the water pump fails for whatever reason.

One thing that must also be noted is that the water pump does not need to be located underneath the aquariun. It can be located to the side or even above the aquarium. The reason I prefer it underneath the aquarium is that it is easier to prime the loop (remove the air). When the pump is above the aquarium you have to suck air out of the tube and this can take a whike – much easier when the pump is under the aquarium.

In my opinion closed loop circulation is fantastic on a [tag-tec]saltwater aquarium[/tag-tec]. You can have as many or as few loops as you want. You can have the outlets in the exact location you want, you can have pipework the width you want (the wider the width the gentler the flow) and you can have more than one outlet per loop.

On another note with the water pump being external to the aquarium a heat source is removed and that has to be good in itself.

So have a think about it. As said powerheads etc can and do work. I have used them with great effect, however I personally feel that you can create much better water circulation in the aquarium via closed loops. For example it would be hard to have power heads at the front of the aquarium pointing up and not look unsightly.

Yet you can with closed loops and a lot more.

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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 Circulation – Go Wide And Soft

With water circulation it is better when keeping sessile marine animals to attempt to produce water movement which is both strong andpowerful yet not hard enough to damage the animals themselves.

Traditional powerheads for example can move a tremendous amount of water around the aquarium, however this is water movement which is not very wide, instead they are rather pinpoint. [Read more]

Water Circulation In The Aquarium – Why Is It So Important

The provision of water circulation in the saltwater aquarium is dependant upon what [tag-tec]filtration[/tag-tec] method you are using and ultimately the life you are keeping in the aquarium.

A few methods as to how to create water movement has been detailed in some previous posts, however I realised that I have never actually gone into depth as to why water circulation is so important.

This is something I hope to rectify with this post. [Read more]

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