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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  1. One thing to keep in mind when planning an over-the-top closed loop system is the possibility of cavitation if the plumbing is too small in diameter. I tried building a closed loop using an Eheim 1262 pump driving an SQWD, using a 1.5″ schedule 80 (I wanted the in-tank plumbing to be grey, so used sch. 80) drain from the tank and ended up cavitating the pump resulting in a serious micro-bubble problem and no obvious solution…

    1.5″ plumbing is as large as I’d want in my tank (for purely cosmetic reasons). Given that, I abandoned the closed loop and (eventually) went to a couple of the controllable Tunze Nano Streams (the 6055 model).

    I’m left with the feeling that the over the top style closed loop works best with lower-flow applications; for high-flow I’d drill the tank or go with stream-style power heads.

  2. Thanks for the input Andy. Personally, if I can get away without tank drilling I will. If I needed high flow (I don’t as I love soft corals) I’d go for the high output stream pumps. There are those who will disagree (fair enough) as they’d say I’m ignoring lower water flow.

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