Swimming Pool. Advice please!


When you say that 'very little action takes place in the actual pool', do you mean that sanitization only takes place in the electrolyser... no, that's not right.

It’s not the electrolyser which is responsible for the disinfection its the chorine it produces. You have to consider that electrolyser as a manufacturing plant - producing chlorine. Un quote:

If you think carefully about it and look at what is happening in the Sterilising unit you will see that pool water is passing through a zone where raw chlorine is being produced, it must be obvious that this is the area where the maximum amount of disinfection is taking place, just as if you tip a container of javel in your pool in one place the concentration and thus the killing power will be concentrated there until the javel spreads through the pool.

I would love to see a total ARS replacement procedure they keep on about!!

According to Wikipédia:

Dans le cadre de la Révision générale des politiques publiques, les DDASS ont été supprimées le 1er avril2010 sauf en Île-de-France où cette suppression n'est effective que depuis le 1er juillet 2010.

In other words no more DDASS.

Erm, no, we don't have paying guests, but others might, hence my comment about my post not being relevant to some.

I think that one detail tends to be , shall we say, "overlooked" when comparing salt water sterilisers with traditional high chlorine pool sterilising.

The sterilising action actually takes place mainly in the electrolysis unit and therefore all the claimed additional benefits do take place because you are constantly re-introducing sterilised water into the pool at a rate of 'quote' 1.5/2m/sec quite a healthy flow in a domestic pool :-), very little action takes place in the actual pool though a free Cl level of 1.5ppm will be sufficient to counter any accidents.Or to paraphrase 'Dirty water in-- Active clean water out'.

And yes until you have experienced a salt water pool, you will not be able to appreciate the silky soft feel compared with javel based systems.

Very impressive 'scientific' facts on the salt v chlorine issue, but it doesn't alter the fact that, subjectively, the water 'feel' is much better with a salt electrolysis system than putting raw chlorine in. Some of our guests knew that something about the water in the pool had improved despite not knowing that I had installed the electrolysis equipment.

(Perhaps not relevant to those who have paying guests using their pool.....)

There is a need to bring some clarity here, there is opinion and there is fact.

They are all salt pools, when sodium hypochlorite (Chlorine) breaks down it leaves behind salt in the water so over a period of time the salt concentration rises and can equal a mild salt concentration similar to that used by a salt conversion proccess, which uses an electric cell to break salt water down into chlorine so that stuffs that argument!

The active chlorine level (hypochlorus acid) in a pool is quite low as chlorine stabiliser cyanuric acid (CYA) bonds chemically to the chlorine to protect it from the suns UV rays which other wise would break down chlorine in just a few hours. This means the active chlorine level could be lower than that supplied by municiple tap water which most people bath in without issue.

What tends to be the issue is the high levels of chlorine experienced in municiple communal swimming pools which is far higher than required in a domestic situation and as is the case with most municiple indoor pools which don't contain CYA stabiliser so the active hypochlorous acid level could be 10x the amount used in a domestic situation.

What difference does that make?

Chlorine will attack anything it will kill bacteria and algae and oxidise and anything else it comes into contact with from hair to skin cells and body oils, sweat etc. That leads to what are known as disinfection byproducts (DBP's) almost all problems related to breathing and skin irritation are actually related to the DBP's and not to the chlorine.

DBP's will occur in both directly chlorine dosed pools and salt water converted chlorine pools and that is down to the correct management of the pool and accurate testing. Because of the lower level of active chlorine in a domestic pool compared to a commercial pool there are correspondingly lower levels of DBP's so it is rare even for eczema sufferers to have a problem in a well managed domestic pool. That doesn't mean it doesn't happen but its rare as clinical chlorine allergy is very rare.

There is some anecdotal suggestion that the splitting of salt water in the cell releases not only the chlorine gas but an active form of oxygen and oxy radicals which also help oxidising bather waste etc, it certainly used to appear in some advertisers information (Ecosmarte etc) but in reality the level would be so tiny and the split molecules of water will re combine very quickly (within 0.5 sec) which at pool flow rates (1.7-2 metres/sec) would mean they never reach the pool so don't really count for anything.

With salt water chlorination you are just generating a tiny amount of chlorine on site rather than transporting it from a shop, however as mentioned above the cells process also produces bubbles of oxygen and hydrogen and these bubbles will tend to cause a continual drift upwards in the pH of the water compaired to a similar dose of directly injectected chlorine. Both forms of chlorine cause a pH drift but it's more noticable with a salt generated version so a pH regulation via a dosing pump should be incorporated.

pH regulation is by the addition of acid of some type, often hydrochloric. That also stuffs the salt chlorinators advertising blurb as they often say "Natural with No Harsh Chemicals" somewhere and that is just rubbish as hydrochloric acid as most peopl know is quite harsh, that said the levels are very dilute so not a worry but advertisers wouldn't let that get in the way of a sale! Both types of pool are a chemical soup and that's the real fact.

It would be quite wrong to propose any suggestion of the "best pool" for your situation without a site inspection. If you are on clay which moves then a proper site inspection will need to take place.

These days fibre glass pools are actually quite rare, far more likely to be a polyester resin as the old glass fibre had issues with osmossis blistering and frequently eneded up requiring a liner. They can "float" out of the ground if the water table gets high or the ground saturated, hence the name "Boat pool". A hydrostatic drain valve can help in some situations. Even concrete pools have been known to float up despite the weight so a site survey and not a forum opinion is the route to take.

If movement is an issue there are polpropelene panel kits and liner combo's which can facilitate movement without damage so there are all possibities.

Don't overlook insulation from your pool design, In the UK all new outdoor pools have to be insulated (Part L of the building regs) because it works. In France however the pool industry is pretty much stuck in time (around about the late 50's early 60's in technology so most pool companies don't have a clue) It may seem silly to some but having your water a few degrees warmer at the ends of the season without resorting to heating would be a godsend and if you are heating it could result in needing a heater with half the output and therefor half the electricity bill. I know enough owners who didn't want to waste money insulating their pools as they weren't going to heat them, only to say something completely different a couple of years on especially as they get older and it's more expensive to do later.

Whilst on the subject of electricity, French built pools are not energy efficient! some are not even efficient, The big 3 pool companies build appalling examples of the flow systems and the water is important, the better kept the water is the less chemical of any kind it will use. Companies with the letters D, W and M at the start of their names should be avoided, they employ sharp suited sales forces and their product are amongst some of the worst pool flow systems I have ever witnessed, yes they have built many 1000's of pools but I should be grateful as it produces work for people like me to go round putting things right but better to have built the thing well in the first place.

What do I mean by the above?

Water has to be pushed around the pool in an efficient way to circulate chemicals and filter out dirt etc. Anything that interferes with that cost you money over the years. There are a rising number of pool companies using mono block filtration systems, the big 3 as mentioned above + numerous others.

What's wrong with them?

These systems are quick and easy for the builders to install and that produces a better bottom line profit for the builder of the pool. For the life of the pool it will be costing you more money though. This is because mono block filtration uses bags or pleated filters etc in front of the pool pump. It is not efficient to suck water compared to pushing water. Water behaves like air, try sucking out the candles on a birthday cake compared to blowing out the candles and you will get what I mean. Highly efficient, state of the art flow design can run your pool on 85%-90% less electricity than a standard pool or mono block filtration system with higher water quality as a result and that allows lower chemical usage which of course means less irritation for everyone including eczema and asthma sufferers.

Have a look at a company called waterair who do kit pools, they are made of corrugated iron with a liner. When I bought my house I thought it had a huge fishpond (covered in black plastic & apparently only a couple of feet deep, plants were growing in the plastic...) anyway after a lot of elbow grease I discovered it is a proper functioning inground pool made by these waterair people who explained how the pumps etc work once I tracked them down on the internet. It is 12x5.5 and there have been no problems with it popping out of the ground etc. I have very very heavy clay soil. I believe it was installed in 1988 so it was 11 when I got it & it is still fine 14 years on...

Salt salt salt. My family have very sensitive skin in different guises, including excema. Everyone has enjoyed our pool with no problems at all. We have found there is a little hard work at the opening of the pool (which is the same as a chlorine pool) but during the season, even with fluctuating temperatures, the salt pool is the easiest to run and maintain. We have had chlorine pools and would never go back.

Ian , just to clarify a salt water pool is just another method of creating chlorine using electrolysis and if you invest in decent kit ( not cheap ) and learn how to keep it maintained then it should perform well year after year - on the other hand i have seen and rectified low grade / poorly maintained kit which failed within a few yrs of the install.

in this area due to ground movement the established pool companies offer a concrete & liner option as standard and not without reasons.

my advice would be to go down this route ,pay extra for a liner arme with frise to avoid staining and damage .

but before anything else buy the swimming pool manual written by Terry Tamminen - although its american the principles of building / water chemistry are the same.

oh and solar was discussed here recently and is of course complex in its own right - and for most basic direct pool water heater systems you will need to provide a solar mat of 50 - 75 % of the pool area !


We have a concrete and liner pool, 10m x 5m. Salt and ph system. We invested in a thicker liner with a long guarantee as we too rent the house for about 10 weeks. Our only regret is not installing some sort of solar heating to extend the season. Looking into it now.

Sorry i don't know is the honest answer, i'm sure someone on here will. It was the immobiliers we bought through who later became our friends who told us when we asked why they were installing an above ground pool in their own garden rather than in ground. Can only surmise it's a substantial amount to make people consider it when deciding. I think as friends of ours have done, if you level it up to the ground on one side then build up to it with decking on the other side/s that it still classes as above ground. And looks rather nice too.

Yes +1 for a salt pool, provided that you install quality electrolyser and Ph Controls, lots of rubbish spouted on some forums but if you read between the lines there is always an axe to grind, ours has been in use for six years so far and no green water, no nasty Chlorine niffs, just azure crystal clean water.

I was never attracted to the glass fibre monocoque, all that water needs a lot of support and it must be almost impossible to provide adequate, consistent support. a reinforced concrete pool, with a liner should overcome your clay problem provided that the base is massive enough so that the structure is capable of moving as one piece.

As for use with a gîte, lock the controls etc. away and appoint someone as guardian/pool expert.

Interesting comment about the above ground approach. We are going to be putting the pool in a sloped area, so are going to have to cut into the slope to level the pool. Are above ground pools as sturdy as those below? How much extra is the tax for putting it below ground?

I forgot to add, our pool sides were built of hollow concrete blocks, reinforcing rods were inserted into the hollows and concrete poured in. The inside face was then skimmed, and a special render designed for pools was the final layer. No need for a liner. I have a series of photos I can let you see if they would help. PM me if so.

Reinforced concrete sides with a strong liner eg Alkorplan should put you in good stead for years. We have used chlorine for years because when we installed the pool we were told that it was going to become illegal to use salt, but it never did. Fibreglass do become a problem with age and if it is possible you will probably have to line it one day anyway.

Can't help you with the dilemma between concrete or fibreglass sorry, what advice i can give we have learned through our experience is don't go too big, our pool was already in when we bought the house, it is a beautiful big in ground concrete pool with roman steps, it's 12 x 6 and 3 meters deep at one end so great for diving, however, being so big it's always a couple of degrees colder than friends who have smaller pools, even 10 x 5 makes quite a difference. We've fitted solar heating panels to help warm it, that couple of degrees can be all important.

If we were going to install another pool ourselves now after having one for a few years we would certainly go a bit smaller and also above ground after learning that an above ground pool that's dug in on one side and decked round to be level with the garden costs less in tax every year than an in ground one.

Ours is chlorine, it was chlorine when we moved in and we've never needed to change it, it's easy to upkeep and doesn't cause any skin problems (one of my daughters suffers from eczema).

Our soil is clay too, prone to movement and our land slopes away so we’ve come to the conclusion that a pool built from Polystyrene blocks that are filled with concrete will be our best bet. We want to get started this summer, haven’t quite decided yet which filter system to use though, interesting comment, Glyn, about the salt water method, will have to investigate that further.

OH has a wealth of experience in the installation of pools - he says that a fibre glass pool is likely to crack if there is movement (they cannot take the changes in stress) and if you put a concrete one in you must ensure that the concrete is heavily reinforced. The same rule would apply to any paving slabs that you lay, they need to have reinforcing rods to make sure that they do not crack.

Cannot help with the salt/chlorine question, sorry.

Salt every time. We started with the chemical route and regretted it after the first year. Whoever is telling you that salt water is more difficult to maintain is talking complete rubbish! If you aim for salt in the first place (ensure all equipment is suitable for salt water) and install silver/copper disinfectant equipment and an automatic pH pump, you'll have nothing to do other than keep the pool clean and use it.

I'm not an engineer though, so can't help with the big question, though our in-ground pool is built on clay and is constructed from reinforced concrete.