'Circulation' is the physical act of moving water around the confines of our aquarium and filtration system. When we talk about this subject we are actually talking about how the system as a whole moves several key items around and the effect that this has on the long term and immediate health of the animals we keep and the general conditions prevailing in any given area of the system. Seeing as there are several aspects to this subject, I have decided to cover them in turn. These are as follows.

1. Chemical balance and the need for stability.

2.Minimising local fluctuations of a detrimental nature.

3.The transportation and Removal of waste products.

4.Replicating the natural conditions essential to the welfare of the animals we keep.

Here Goes.

1 Chemical balance and the need for stability.

As stated in the previous section, the water we keep our animals in, is a soup of different chemicals, each directly linked to each other and dependant on a stable balance. By mixing this soup at a reasonable rate we ensure that the levels or 'concentrations' of each part (element) of that soup are evenly dispersed throughout the entire body of water no matter where is is within the system as a whole. If we allow one area of water to become stagnant then that body will change its chemical composition due to the effects that one element has over another.

The best example is the effect Co2 has on the Ph of the water within the tank and the relationship between surface movement, bio load and Ph.

If we take any given Aquarium, complete with its assortment of precious organisms and turn off all the pumps so that the water movement around the system stops. After a while we will notice that the Ph of that water slowly drops off without any addition, or interference by ourselves. The reason for this is that all higher forms of organisms i.e. those above algae and plants, require Oxygen to fulfil their respiration requirements 24 hrs a day. The by product of this process among others is the production of Co2 or Carbon Dioxide. this gas has a negative effect on the Ph of our water and gradually pulls down the Ph till we have gone from Alkaline to Acidic. Obviously not very good for our inhabitants, and in the case of fizzy pop or carbonated water...not very good for your teeth. Algae on the other hand use Co2 during the day and produce O2 as a by product, and at night they use O2, and give off Co2. excellent so we are saying that if we keep lots of algae the O2 is replaced during the day and Co2 is reduced and that will keep our Ph up.....Well not quite. remember the other organisms are only using O2, so the balance between the producers of CO2 and the producers of O2 is not very even, hence either a downhill slide in Ph over 24hrs or a drastic swing over 24hrs in the case of tanks utilising large amounts of algae.

The best place to get rid of Co2 is at the air/water interface, or the top of your tank. However the surface of water is a little tough at the best of times ( a little like the skin on a rice pudding in molecular terms) as such it doesn't want to let things pass through it. By agitating the surface we effectively stop this skin or surface tension from forming and make the passage of dissolved Co2 possible back to the air above. At the same time we enable oxygen to pass back into the water from the air above to keep things at a happy medium. effectively an air stone, skimmer, spray bar, or power head all fulfil the same requirement i.e. to provide effective agitation to increase the air/water interface for the expulsion/addition of the relevant gases so that equilibrium is kept and Ph is maintained at stable levels.  Pointing a power head or pump outlet across the surface of the tank is essential for ongoing health and stable Ph.

So, rule 1

1.'Good circulation and surface movement keep the balance between O2 and Co2 at favourable levels'.

2 Minimising local fluctuations of a detrimental nature

In chemical terms the above is also relevant in that when we introduce additives to our tank or perform a water change, the difference in chemical composition will effectively hang where we added it, until such time that we mix that area with the surrounding water. The danger of not circulating this new water or additive immediately is that any animals that swim through or are trapped in it will suddenly find that they are in conditions that differ severely from what they are attuned to. This will cause stress and possible injury. We therefore need to remember  rule 2.

2 Good circulation keeps chemical differences and variations to a minimum throughout the system, thereby ensuring a chemically stable environment for the organisms we keep on a moment to moment basis.

3 Transportation and removal of waste products.

One of the main reasons why we need to have good circulation, is to keep our system clean and healthy. Any area that is slack or stagnant will be a place where waste material, 'detritus, uneaten food, and faeces' build up. This then breaks down and increases the levels of dissolved organics present in the system and increases the risks of algae outbreaks if the systems biological processes are interrupted for any reason such as salinity drift etc. This can be between, under, or around rockwork, in the far corners of the tank, or in severely under circulated conditions cause a general coating of all surfaces with the aquarium leading to massive outbreaks of problem algae i.e. hair and red cyanobacteria. This coating also smothers the live rock we use, blocking its pores and prevents it from performing its main function as a filtration medium. Now it would be very easy to just simply whack in some of the biggest power heads we can find, turn the whole set-up into a raging torrent and think we've solved the problem. Well as with most things fishy, there is always a compromise to be met and other issues to be considered. the first being our animals i.e. some like SPS corals and Tangs will love this type of environment with a strong surge. However corals such as bubbles, or other LPS species wont appreciate being battered about by an unrelenting tidal wave action 'although it is possible to combine these two environments in one aquarium with some careful aquascaping but I'll come to that later'. The second is our filtration system, which at different places requires different conditions to work effectively.

In tank, and Sump circulation/flow rates, and what they mean.

Remember that one of the main aims of having good circulation is to keep waste material moving, and in suspension till it reaches the parts of our filtration system that are able to deal with it i.e. our live rock, skimmer, and DSB or plenum. the way in which each area deals with waste is slightly different so our flow rates need to take this into account.

Live rock primarily breaks down dissolved chemical waste in the form of Ammonia, Nitrite, and Nitrate etc. it is therefore essential that a high flow rate over the rockwork be maintained so that this waste is carried across and through the rock so that it be broken down and at the same time sufficiently strong that solid waste is not allowed to settle on the rock so that it blocks these pores. Although live rock does harbour a multitude of detritus eating organisms they are quite happy to migrate to areas where this waste collects unlike the rock itself that cannot keep itself physically clean. At the best of times these organisms can only deal with a certain amount of collected or settled waste. so here comes the next rule.

3 In order to maintain the health and cleanliness of live rock and the system as a whole. Good circulation, over, through, and around the rock is essential.

On the type of set-up I'm talking about here (Please don't shout all those that utilise the 100% natural approach) the skimmer or 'foam fractionators' is an integral part of the filtration system, so it should always be placed in a location that allows it to take out waste as early as possible in the filtration process i.e. before the DSB. 'There are other reasons but I'll come to that later on the DSB and Live rock page.'

The sump based DSB has its own requirements that determine how we flow water across it. In practice the DSB is a very efficient waste bin and compost heap, another words we let waste material settle here for the sole purpose of feeding the multitude of organisms present, which actively rise up through the sand layers to the surface to drag down and consume anything edible that has settled there, this movement is what keeps the sand bed healthy and from going stagnant. To achieve this 'settlement' we need to slow things down a little so that suspended particulate matter ' faeces, food, and detritus, has time to fall out of the water column, and settle on the surface of the sand bed ready to feed the inhabitants, although not so slow that the sand bed is not getting a good supply of freshly oxygenated water. again 'compromise'. (In-tank DSB's are effectively governed by the prevailing conditions within the tank itself, but its fair to say that even in tanks with a high flow rate there will always be stagnant areas especially around the base of rockwork, were detritus can collect to feed the bed thereby simulating what we are doing when we slow the flow rate down in our sump based method). So here is the next rule.

4 A sump based DSB needs a slower flow rate than other areas of the system to enable waste material to settle and be utilised as food for its inhabitants. Another words,  give the bed 'time' to feed!.

4.Replicating the natural conditions essential to the welfare of the animals we keep.

Both corals and fish are attuned to differing types of conditions i.e. Tangs predominantly come from surge zones where flow rates are extremely high as do most SPS corals. Mandarin fish sea horses and most LPS corals fall allot lower in the flow rate chart, coming from areas of mild currents where life is a little slower and things are little more gentle. Other factors also come into play when we talk about flow rates that directly influence how our animals behave and whether they thrive or not. Most corals be it soft or hard are covered by a thin layer of mucous that is there to either inhibit the growth of algal films (ref the waxy coating frequently shed by leather corals) or as a method of collecting organic food particles to compliment the additional food gathered by such methods as stinging tentacles (fungia's are a prime example of these combined methods) It is also very common that these mucous coatings are toxic in nature as an inhibitor to neighbouring species or to protect against invasive algae's. So we therefore need to take these factors into consideration when planning what type of animals we wish to keep and how we are going to house them. By far the easiest method is to settle on one biotope and stick to those species found only in those areas. however by simply arranging one or more areas of the decor to act as a surge break or deflector it is possible to combine the two together quite happily as long as food requirements are met and the above rules are not broken. By moving water around our animals we are effectively bringing nutrients to them in the form of food or chemicals and taking away unwanted waste materials. Unfortunately, most corals lack the ability to actively hunt down prey or food, so they therefore rely on the surrounding currents to bring it to them as well as life giving Oxygen essential for the respiration process.. However as stated before, compromise is the key word. A good analogy is the 'Cadburys cream egg' scenario.

'If I were to throw a cream egg toward you 30 times, the first 10 being under arm at a very slow rate, the second 10 being at a moderate rate, and the final 10 being a full blown hurling session. Its fair to say that your success rate at catching the egg on the first 10 throws would be high, although the frequency that you are receiving it might starve you eventually. The second series of throws would see you happy and contented with chocolate dribbling down your chin. Your success rate would again drop down immensely during the last 10 throws due to sheer velocity alone and starvation would ensue'. This is much the same problem that corals have, i.e. the speed at which food is thrown at them is crucial to their growth rate and ultimate survival. Again there is a Compromise to be met!

Looking at corals in detail shows us that they are used to receiving food from nearly all directions. This is evident from the fact that the polyps on SPS corals are spread over the entire surface of the branches and not just on one side. 'mother nature doesn't bother putting mouths where they are not going to get any food'. So this also means that a 'varying' flow pattern is just as crucial to success, as outright flow. So the next rule is as follows.

5. Flow rates and patterns within the confines of the aquarium must fall within the boundaries of the original conditions our animals are used to in order to meet their biological needs.

Ok, Ok, I get the drift, so where do the power heads go and how many?

Well the simple fact is that there are no hard fast rules when it comes to 'HOW' you move water round your system, because rock arrangement, tank dimensions, sump capacity, 'and overall design' all play a major part in how this body of water will behave. IMO for 'in tank' circulation you can go for the flexibility and ease of multiple power heads with the current variation being controlled by a wave module, or by using individual timers on each power head. Or you could look into 'Closed loop' systems consisting of a large external pump/s putting out through multiple outlets placed at strategic points around the aquarium, this works well with the added advantage of heat reduction because the pumps heat goes into the air, rather than the water, although the drawbacks are such that if the pump fails your corals are effectively dead in the water whereas a single power head going down is no big setback. '

Using my old 200 gallon system as an example.

I decided to go halfway on this setup, and mount five Aquabee 3000's externally as separate closed loops, taking water from the tank down to the pumps and then strait back via return pipes, spay bars, and nozzles'.  How powerful, and how many you need, is determined by the volume of water you wish to keep moving around, so all that waste stays in suspension till it gets to your sump and is removed by filtration equipment. Fitting flow taps on each line will give you ultimate control over flow patterns, and velocities to ensure they fall within the boundaries of what your corals need to stay healthy.

NB (Pic 1.). It is very common that with cheaper powerheads the manufacturer will fit a small bore nozzle on the output to give the impression of stronger flow 'A'. The drawback to this, is that this type of output lacks the ability to cover longer distances due to its narrow jet. The other downside is that this type of flow can also be quite cutting/harsh for some corals (even to the degree it will tear flesh from some fleshy bodied LPS corals). For our purposes, 'larger bore' high turnover powerheads, or circulation pumps 'combined with wide bore closed loop plumbing' is far better at shifting water around in a 'strong, but even' flow. This is more in line with the type of conditions our corals are used to in the ocean 'B'.

PIC 1.

See Also.....  DIY 5  and  DIY 6

The term 'flow rate' is a little misleading in this respect, in that 'flow rate' is a measure of the velocity of the fluid, over a given distance i.e. meters/second. A far better way is to talk in terms of 'turnover' or the rate at which the water within the confines of the aquarium is moved/cycled around the system or section involved, i.e. gallons/litres per hour, or cycles per hour.

When we talk about turnover, we are effectively talking about the number of times per hour that the contents of our system is routed through either the circulation devices (power heads/closed loops) or through the sump, but remember different areas of our system require different rates to achieve our goals.

For 'In-tank' circulation we need to combine the total output of all circulating devices 'including' the output from any return pumps that are feeding water back to the aquarium, as these also add to the total turnover or 'motion' within the confines of the tank itself. As an example I'll use my new set-up to paint a picture.-

Total tank volume not including sump = 145 gall or 550 ltrs

Combined output of 5 Aquabee 3000 circulation pumps and 2 x Aquabee 3000 return pumps = 21,000 ltrs/hr

this gives a total turnover of 38.18 x tank volume per hour.

NB. the figure quoted for the return pumps does not take into account the head loss. This is just an approximation.

The same results can be obtained by using only 3 power heads of 6000ltrs/hr output combined with the return pumps so in the end it boils down to individual choice. Now it might seem that 21,000 litres of water whizzing round sounds like a veritable whirlpool, but remember that tank dimensions and rockwork can have a significant effect on this flow, and slow it down or deaden it considerably. This is why the above thought process is so important, because there is no exact figure of turnover that can be stated for all cases only a start point as a rough guide. If you ever get the chance to visit a real reef you will be astounded at the force of the wave action over SPS corals at the reef crest and come away wondering how you can replicate this in the home aquarium. Well in real terms we cant, we can only try to replicate as closely as possible the flow patterns and  get as close to normal flow rates as possible with the limitations placed on us by sheer size alone. Suffice to say that big tanks need big pumps to get the force behind the flow and to carry it the distances involved whereas smaller tanks need proportionally smaller pumps to achieve the same results. There have been several innovative ideas around to replicate reef surge such as dump buckets or surge tanks, although for my purposes they are prohibitive due to space and the effect that they have on auto-level controllers and top-up systems, not to mention noise in some cases.

As a rough guide, to what type of flow may suit your needs you could use the following as a benchmark. 'In-Tank' turnover rates of 10x/hr for softie dominated tanks, 20-30x/hr is advisable for mixed LPS/SPS/Soft coral tanks, whereas 40+ is not unusual for SPS tanks that need a high turnover rate to meet the corals needs and to promote proper growth. but remember that with very large tanks, that may not be possible. In some cases its possible to get lower flow rates but but more powerful surge by using very high output pumps with very wide bore outlets. In this case, total velocity of flow may be down, but the power behind that flow is considerably greater. i.e. the Sequence pumps that give out 10,000lph, but use a 40mm outlet.

For Sump turnover we are looking at things from a slightly different angle. In my case, I am utilising a sump based DSB that according to rule no 4 needs a flow rate that enables suspended waste material to fall out of suspension and settle on the sand bed for long enough that the organisms involved can feed on it. Back to the maths then.

Going back to my 200 gallon setup, we need to remember that the 2 Aquabee 3000's are taking water from the sump back up to the tank at a rate of approximately 6000 ltrs/hr. With a sump of only 36 gall or 136 ltrs this means that the movement of water through the sump itself is 44 x the sumps volume/hr. This is higher than the tank turnover and to a certain degree, means that the water present is travelling at nearly twice the velocity of the water in the tank due to the smaller/ confined pace that is only 12" wide rather than the tanks 24" width. MMMM. at this rate, suspended waste will travel so quickly through the sump and DSB that it wont get a chance to settle and will end up back in the tank again unless its removed by the skimmer. To this end the design of the sump itself is crucial to success, I therefore needed to use baffles to cause a speed reduction over the DSB or in 'this case' raise the DSB up slightly and out of the flow to feed it separately from a 'Tee' that takes water from the main overflow pipe where all that lovely food is hurtling down to the sump from the main tank, then into the DSB to settle at a flow rate I can control. This water then overflows back into to the main sump and to the return pumps. the skimmer takes out the surplus.(see this page  DIY 4 )

This gives the following figures.-

In-tank turnover = 38 x tank vol/hr or 21,000lts/hr

Sump flow rate = 44 x its own volume / hr or 6,000 lts/hr

DSB flow rate of approx 2520lts/hr teed off from main overflow pipe and fed from skimmer outlet.

In terms of total tank and filtration capacity the following figures apply.

Total water volume in system. = 686 litres

Total 'system' turnover through sump = 8.7 times per hour.

Total system turnover through DSB = 3.6 times per hour

Total system turnover through skimmer using an Ehiem 1260 feed pump = 1.8 times per hour.

The diagram above represents a rear view of  the full circulation system as follows.

Pump A is the feed pump for the skimmer

Pumps 'B' Are the 5 main closed loop pumps

Pumps C  are the main sump return pumps exiting via two swivel nozzles mounted in the back panel.

NB.      As of September, I decided that a fifth closed loop was to be added, which again draws from the centre/top of the tank, and then feeds back, via a buried 21.5mm pipe which runs along the front of the tank. This tube will have three outlets in the form of swivel nozzles that exit just above the surface of the sand bed at a 45 deg angle. These nozzles will push water 'up' the rock face in an effort to mix water from the lower regions of the tank with well oxygenated water from the upper layer. Although this might seem a little overkill, I 'and others for that matter' hold true to the theory whereby some systems suffer from what I like to term as 'repetitive flow syndrome'. This is where the only circulation with the tank, is of a horizontal nature. this I feel is strongly connected with the frequent cyano/slime algae outbreaks people commonly complain of over sand beds, even though their water quality seems fine. Its this lower (stale) layer that is just going round and round in one big circle without actually mixing or being replaced by the higher quality water from the upper regions that's causing the problem in my opinion. I will add photo's of this part once added to the system.

Summery

As can be seen from the above figures filtering and moving a body of water requires attention to detail if we are to take into consideration the rules we laid down earlier. It also becomes apparent that the bigger the volume the harder it is to keep these areas covered effectively. But with careful planning and a little bit of maths its easy to prevent costly mistakes before filling the tank up and then discovering that we have broken one of the above rules.  The figures quoted above are in no way set in concrete but are aimed at giving some insight into what we are trying to achieve, by differences in design, livestock, and layout, any of the above figures may be changed to suite our needs, however we should always remember that they are separate issues, with each area requiring its own individual attention.

So the final rule would be as follows-

6. Don't just go out and buy the biggest pumps you can find. plan your set-up before you start, and look at each aspect in turn to ensure the best possible conditions for your animals etc.

Have fun.........

For more Info on Plumbing your own system and in depth details on how I did this system. look at this page ...  Plumbing

For details on 'large bore VDL plumbing' and 'Sequence pumps'. look at the new system.