What filter and pump system should we be starting with?

Hello. Now planning for new build 8m x 4m x 1.5m below ground pool. Second home. Used 4 months of the year. Family only.

At the moment it’s not the pool I am most concerned about, but the electrical and mechanical and other bits needed to keep it clean and safe, economically. I think I should avoid ‘monoblock’, but aside from that I am at a loss.

Any pointers please? What should I be asking for?



@Corona this is your area, isn’t it ???

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Hi Graeme, yes avoid a monoblock, easier for the installer but harder for owner going forward.
For that size of pool I would have 2 skimmers on the longside, 4 returns oposite making sure there are no dead spots in the corners. Main pipework in 63mm. A variable speed pump with a 600 dia minimum sand filter with a side mounted backwash valve and filled not with sand but Dryden Aqua’s AFM ng glass media, it is the best. Pipework should use radius bends or 2x 45 degree bends where needed rather than sharp 90 degree knuckle bends. Water treatment wise you could have a salt water chlorinator with possibly the hydroxyl generator, these are definitely the future for water treatment over standard chlorinators. Or direct chlorine dosing but regulations are forever tightening on the transport and purchase of javel chlorine so I am switching on my own pool. It would allow a degree of automation as well. Are you adding a heater etc? Those are the basics. What type of construction are you going for, I would always recommend insulating the pool for good heat retention and a good bubble cover ( Geobubble) and winter cover, not the mesh variety.


This is terrific information. Thank you very much John.

I have read your advice elsewhere about the benefits of improving the efficiency of water flow through pipes, so think I understand that.

You mention ‘no dead spots’, any advice on how to avoid them at planning stage please?

Regarding pump, filter, chlorinator, hydroxyl generator and automation. (Automation is desirable as it is a holiday home.} Is there a single source for all these items or a brand to look out for? Would I need an expert to specify exactly what is needed? I am thinking I would as while I can do basic plumbing this is all completely new to me?

Our garden is sloping with limited access across a fosse that has overhead power cables. We have been told the access (in particular overhead power cables) prevents one piece pools from being installed, so it will be a constructed pool with liner. I have started to investigate IFB construction but so far am not convinced the expertise exists locally or even at a distance. However I am bearing in mind the need to insulate, but don’t know how to do so with normal blocks. It’s important to me I understand the construction as I want to be able to discuss with local companies who insist on doing the job in the traditional ‘always done it that way’ method.

Heating - yes. Thinking of a stand alone heat pump.

Cover - some sort of manually operated slatted cover on a roller? I imagine a geocover would go on top of that?

One more thing about pipework. Should we have a drain in the base of the pool? If not how is the pool emptied when necessary?

I hope my questions are of interest to other forum members, if not then may I contact you directly please? I am near Bergerac.

Thanks again


Hi Graeme,
To avoid dead spots is placing a return where its flow would reach into the corners to circulate the water, think of it as a snooker table and how a ball would bounce of the cushions would give you an idea but of course a pool has depth as well.
Your pool builder will likely as not purchase equipment from the wholesalers without much knowledge or care sadly most simply do not understand more than the basics. The biggest issue I came across was me the Englishman is doing the local technique? Usually followed by a Galic shrug or worse a total strop. One particular job it became quite heated and although the pool company was building they also used the wrong grade of pipe for burying and 1 week later a pipe had been squashed and they did not want to come back to repair so just gave money back.
Moving on, As Fluidra have bought up a large proportion of the pool equipment manufactures how that now effects their supply chain buying choices I dont know but I have always cherry picked the best parts I could find from across the globe and done bespoke installs.
A lot of pool builders have experience with polyblok type construction which is probably the easiest, there are companies like Nudura who may have a builder near you. If they do insist on concrete block then lining the structure with extruded polystyrene is an option and brico sheds stock this and also the Wedi panel type of insulation which is incredibly strong.

Heat pump is a good option, look to match its flow rate to a similar flow rate for turning over the water, thankfully most are in this range but best to check.
Personally I dont like statted covers on outdoor pools as the dirt gets in and they can be a devil to get clean, the Geobubble as mentioned before is much easier almost self cleaning because of the shape of the bubbles with no corners. You would need a roller for that albeit a lighter construction one compared to a winter cover. they just float on the water preventing heat and water loss.
Winter cover, depends on your budget of course but one stands head and shoulders above the rest of the manual ones, just check its not the mesh cover they are selling, watch the video its simplicity itself for these slightly awkward heavy covers or you may be thinking motorised?

Main drains do very little apart from draining, I prefer a submersible pump to a main drain but where clients have requested one I usually plumb them as both inlets and via a valve into an outlet as introducing warm water lower in the pool give a better warm water without stratification where the surface few inches are warm but the deeper part is still cooler, the same can be acheived by mounting two returns a bit deeper as was often done a few years ago.
Hope that helps a bit more.

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Adding to that, I would suggest that you go for an upmarket filter - Hayward or the like. I was looking at an unbranded filter in our local shop t’other day, and boy, the feel quality of the multi-valve left a lot to be desired :rofl:

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Thats also true of some branded makes these days, cost accountants are everywhere. Its also why I recommend side mounted valves because they are much easier to change, I invariably do change the multiport for something better waterflow wise as the torturous route the water has to make robs a lot of flow and hence requires a bigger pump. 99.9% you are in filtration a valve arrangement that favours that position saves a lot of energy that would otherwise be wasted.
Similarly air assisted backwash save a lot of water and does a better job, try asking your local pool builder for that little trick and they would just look at you blankly.

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I look at you blankly…!

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I think we call it continous improvement and the huge water saving on backwash justifies it, give the rest of the industry 20 years and maybe they will embrace the changes.

i still look blankly! What is the air assisted backwash trick?

By introducing high volume low pressure air into the backwash flow you air scour the filter media. Domestic filters do not backwash well and from experience a fair amount of fine silt can often remain. Sand requires 60m3/m2 of filter area so an average 600mm dia filter (0.3m) requires 20m3 flow to backwash it, (AFM 45m3/m2) thats a lot of water used to eject what is essentially a small amount of dirt. Water treatment plants use air scouring to seperate the grains of sand and dislodge dirt etc. By using cheap air rather than expensive and in some cases scarce water I aimed to achieve the same thing. I would with basic math reckon on using a 1/4 or less water to backwash than using just water alone. Varying the air supply allows tuning of the filtre bed expansion so as to not loose the media but also achieve a much better backwash and therefore cleaning of the filter media.
Just more ways to reduce energy and waste on domestic pools.

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We used the process in our factories, if it’s the same process in a pool environment then this might explain how it works.
Research has shown that water-only backwash is a weak cleaning process as grain collisions are minimal. It is more effective to include air flow in the cleaning process.
The use of air scour
When air scour precedes the water wash, it is intended to break up and detach deposits ready to be flushed out.


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Yes, however with sand its not so important to not damage the surface, AFM is actually 300 times the surface area of sand so we want to expand the filter bed to release the dirt etc but not abrade the surface of the AFM too much, hence why I changed the term to air assisted backwash rather than air scour. By using a small flow of water simultaneously to wash away contaminants but allowing air to do the bulk of the work.
Its not done at all in the domestic pool market but domestic filters do not backwash well.

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Sorry for no response over last few days, been en route to UK. I need to study the extremely useful advice given in this thread and no doubt will have more questions. Many thanks John @Corona

No problem Graeme, heading that way again in a few days. Just want you to get the best result for your pool.

Just out of interest (and for future reference), how and where is the air introduced into the backwashing water?

I have mine after the backwash valve as previous positions didnt work as well. An spa air blower with speed control to adjust the flow.

How does that work on a 5 or 6 way valve.

In your case you’ll have to extend the pipes from the valve to the filter and fit a swept T in the lower pipe provided its a side mounted valve, if its top mounted you’ve had it.

OK - read through everything! Which is not the same as understanding.

So I will plan for a variable speed pump, 600 min dia filter fitted with a sidemounted backwash valve and filled with Dryden Aqua’s AFM glass media, chlorinator, hydroxl generator, and automation. Plus a stand alone heat pump and lots of 63mm piping with radius or 45 degree bends…

But there my plan ends. How do I join all the bits together? (It will also affect the size of the hole thats dug outfor the pool?)

Next to the planned location of the pool is a good shed with windows that I think will be our pool room. Its only 4m away. However, the floor of the shed will be above the water level in the pool. Most of the pool rooms I see appear to be below the pool water level. Is that a problem?

Are these issues something you could help us with please John @Corona - paid for of course. (Please do DM me if you prefer)

We are just going through the process of installing a new fosse septique that will create space for the pool. SPANC have approved the plans for the new fosse, but we are thinking that the garden will be in such a state when that is being done we might be better to get the pool hole dug out at the same time. So the planning for the pool is more immenent than we had originally thought.