bluepools

Swimming pool water chemistry

Introduction

As it is a holiday and I have some spare time from pool installation I thought I would add some more detail on water quality following our posts on this topic in October. This is the first on a series of posts that will end with a commentary that is a very hot topic in the pool industry - the move towards salt water chlorination.

pH

pH is the single most important element in swimming pool water chemistry. It affects every other chemical balance in pool water.

pH is a measure of hydrogen ion (H+) concentration in water. It indicates the relative acidity or basicity of pool water. pH is measured on a scale of 0 (strong acid) to 14 (strong base) with 7 being the neutral pH.

In pools a slightly alkaline pH of 7.4 to 7.6 is apparently the most desirable because this range is most comfortable to the human eye and provides for optimum use of free chlorine while maintaining water that is not corrosive or scale forming - but this is not always true as we will see in later posts.

If pH is too low (below 7)

• Water becomes acidic
• Chlorine residuals dissipate rapidly
• Eye irritation occurs
• Metal fittings, pump impeller, heater core may corrode
• Dissolved metals may leave stains on walls
• Rapid Loss of alkalinity

If pH is too high (above 8)

• Chlorine activity is slowed and inefficient
• Scale formation and discoloration of pool walls
• Water becomes cloudy
• Filter is overworked
• Eye irritation may occur

pH Adjustment

To avoid the problems listed above, pH must be maintained between 7.2 and 7.8.  If the pH is too low raise it by adding pH Plus (sodium carbonate) at the recommended dosage for the pool volume.  Be sure the pump is running when chemicals are added. Allow to recirculate then retest to determine if further treatment is necessary. If problems with low pH persist, it may be necessary to raise total alkalinity to stabilize the pH.

Total alkalinity (TA)

Total alkalinity is closely associated with pH but it is a measure of the ability of a solution to neutralize hydrogen ions. Expressed in parts per million (ppm), total alkalinity is the result of alkaline materials including carbonates, bicarbonates and hydroxides - mostly bicarbonates. This acid neutralizing (buffering) capacity of water is desirable because it helps prevent wide variations in pH whenever small amounts of acid or alkali are added to the pool.

Total alkalinity is a measure of water's resistance to change in pH.

Total alkalinity in a swimming should be maintained in the range of 80 to 150 ppm.

If total alkalinity is too low:

pH changes rapidly when chemicals or impurities enter the water. pH may drop rapidly, causing corrosion etc.

If total alkalinity is too high:

pH becomes difficult to adjust. High pH often occurs causing other problems such as; cloudy water, decreased disinfectant effectiveness, scale formation and filter problems - more on this in later posts.

Total alkalinity can be raised by the addition of soda ash (sodium bicarbonate, baking soda)  - there are other proprietry products on the market that are even more effective - just follow the instructions on dosage.

Total alkalinity can be lowered by adding muriatic acid (hydrochloric acid) or sodium bisulfate or other proprietry products.

Just remember your pool water will only be OK if the pH is right - and that will depend on total alkalinity.

Will Witt

Swimming pool. Charente Maritime, France

The swimming pool at Cherac, near Cognac, Charente Maritime is nearing  completion. The pool has a sand coloured liner with Carthage Vert tile band and sand coloured roman end. The paving is Ardoise Jaune by CaraTerra and is installed with the margelles flush and all joints lining through to give a finish that is very pleasing to the eye. The pool has been fitted with a winter safety cover and will also be protected with a pool safety fence by Encloture. The pool filtration, sanitisation and heating system comprises a 0.75CV pump, 600 dia sand filter, in-line chlorine doser and 12kW heat pump. The photos show the pool nearly filled and ready for the skimmers to be installed. Notice how the sand coloured liner makes the water appear turquoise which can help marry the pool into the natural surroundings.

Swimming pool complete. Dordogne, France

The pool at Serres et Monguyard, near Eymet, Dordogne is now complete and is very similar to the pool we recently completed at Monteton for the same client. The pool has a sand coloured liner with matching roman end and Sahara margelles. The pool has been fitted with a winter security cover which will be augmented with a pool safety fence in the spring once the paving has been installed.

The pool house is also very similar and is fitted with a 1CV pump, 600 dia sand  filter, saltwater chlorinator, pH regulator, pump/light control box and 12kW heat pump (installed out of sight behind pool house).

Swimming pool complete. Lot et Garonne, France.

The swimming pool at Monteton, Lot et Garonne (between Duras and Eymet) is now complete.

The photos show the pool just before grouting of the margelles. The liner is a uniform sand colour with matching roman end. Installation of the paving has been deferred until spring to allow for settlement of the backfill around the pool.

The pool has been fitted with a temporary alarm which will remain in place until the safety fencing is installed next spring.

In the pool house you can see the 1CV pump, 600 dia sand filter, saltwater chlorinator, pH  regulator, control valves and pool filtration/light control box. A 12kW heat pump has been installed adjacent to the pump house.

Pool near Cognac

Last week I promised that I would keep you updated on the pool that we are installing near Cognac in very difficult ground conditions. The first picture shows what happened when we started to excavate for the main drain under the hopper that we installed last week. The water eventually rose to the top of the trench - see the fourth picture.

The second picture shows the drain excavated down to 500 mm below the bottom of the hopper. The geotextile that will stop any fine material from clogging the drain and the 300 mm pipe that will act as the pumping chamber have been installed.

The third picture shows the drain filled with stone.

The fourth shows the foundation to the walls of the pool ready for concrete - we managed to pour the entire wall foundation on Friday despite a day of rain. It also shows that the groundwater table is at about the top of the hopper.

To build the hopper we will need to run a submersible pump at the bottom of the concrete pipe pumping chamber continuously until the liner is installed and the hopper is full of water.

The moral is - if you live in a valley - especially near a river or stream - you need professionals to build your pool.

Until next week.

Will Witt

Bad ground conditions

We have just started a new installation in the Cognac area. The land is quite low lying and beside a stream - so we anticipated that it might be quite problematic.

And it is!

The top metre is filled ground, underlain by very soft clay with running water at the bottom of the fill. We are contracted to install a 1 metre deep hopper.

We have already decided that the pool floor will need to be in reinforced concrete, and we are now working out how to build it underwater!.

Joking aside we will install an underpool drain with a submersible pump to allow us to dewater the excavation and this will be left in place for the client to dewater the surrounding strata whenever he needs to empty the pool.

This is just another saga in a long list of installations where a kit type pool would either be impossible to install - or would fail during the first time that it is emptied.

We will let you know how we get on with this project next week.

Landscaping to swimming pool at Indre, France

The landscaping to the pool we recently completed at Indre is now finished and as you can see, the pool looks absolutely stunning in its mature garden setting.

Bluepools launches its new range of pools with an unqualified lifetime structural guarantee

The new website gives a full description of the pools that are insulated to keep the water warmer and allow extended use of swimming pools in France in summer. Roman Ends, covers and top quality components are all now included in the standard Bluepools range of pools.

Jonzac, Charante-Maritime, France October 15, 2005 -- Bluepools has now completed an intensive three year long research project into the best type of swimming pool for its primary market in South West France. The firm intends to extend its installation capacity across France by the end of 2006 now that it has identified the optimimum approach to the provision of very high quality, structurally guaranteed swimming pools that provide the best value for money. The new website is www.bluepools.co.uk

The firm is managed by a father and son team of qualified civil engineers and is uniquely capable of analysing the soil conditions at each different sites where it has installed swimming pools and other works. Their research has shown that at 8 out of the 10 sites the subsoil consisted of filled ground or alluvial clay. The limestone rock that dominates the geology of SW France only occured at 2 of the sites. The rock is always there - but invariably at a deeper depth than the foundation of the pool

The proponderance of the fill and clay subsoil has serious implications for the suppliers and installers of kit and liner pools.

They are not suitable in filled ground because of the highly variable weak soil conditions. They are also not suitable for clay soil condition because of the clays tendency to expand when wet and shrink when dry. When a large hole is dug in clay subsoil and a pool is installed, the void around the pool that is normally back filled with gravel by kit installers, will inevitably fill up with water in winter like a buried ditch. The combined swelling clay and water pressure can cause the liner to lift off the pool wall and perhaps even the collapse of the pool walls.

Bluepools now provides a lifetime unqualified structural guarantee on its polystyrene block reinforced concrete pools. There are now a variety of dense polystyrene blocks available in France that are used for the construction of swimming pool walls . The blocks are normally between 1m and 1.5m long, 250 mm wide and 250 mm deep. This allows the construction of pool walls either 1m, 1.25m or 1.5m deep with greater depths provided by a hopper at one end that can provide up to an extra 1m of depth. The blocks are erected on a reinforced concrete footing and then filled with reinforced concrete to provide a very stiff and rigid wall that is very quick and easy to install and is suitable for all ground conditions. But even with these very strong walls Bluepools always installs both sub-pool and wall perimeter drainage in every pool that it builds.

It was a happy co-incidence that the blocks not only provide a very flat and true surface for the liner to lie against but also 100 mm of insulation that makes the pool water warmer and cheaper to heat.

In its pursuit of providing the best value for money in France, Bluepools incorporates the best quality pool furniture, filtration equipment, covers and many other element that other pool installers charge for as extras. The optimised filtration equipment provides pool water turnover in 6 to 8 hours and this ensures that the pool water is always healthy.

For more information please go the website at www.bluepools.co.uk

The importance of pH

Previously, we recommended that you not add chlorine to the pool until you've checked and adjusted the pH level.

The reason for this lies in the chemistry of water and what happens to chemicals in pool water. Chlorine forms hypochlorite when added to water. It is the hypochlorous acid (also known as free chlorine) that does most of the disinfecting work.

The proportion of useful hypochlorous acid and the not-so-useful hypochlorite ions is indicated by pH. For instance, at a pH of 7.0 the prescence of hypochlorous acid in the water can be as high as 80 percent, with only 20 percent present as ineffective hypochlorite ions.

When pH is allowed to drop to 7.0 the water will be too acidic for comfortable swimming, and at this level, it will attack pool surfaces and equipment. The recommended pH range for pool water lies between 7.2 and 7.6; this allows the most economical use of chlorine without putting the water out of balance.

If the water is allowed to reach a pH of 8.0 or higher (and it is not unusual to find this in private pools) you will have to maintain two to three times the chlorine residual to produce the same amount of sanitizing hypochlorous acid.

Superchlorination of your swimming pool

Superchlorination is simply an extra dose of chlorine - a kind of shock treatment - to burn out bacteria, algae, nitrogen compounds, and especially ammonia, all or some of which have not been elimated by routine chlorination. Three to five times the normal dose of chlorine is added to the pool as directed on the product instrucitons. Increased bathing loads and increased algae growth during summer months, when unheated water may reach a temperature of 30 deg C or higher, may make superchlorination necessary. You may need to superchlorinate when bad odours or algae (green or coloured water) are visible, when bathers complain of eye irritation, or after the pool has had a period of heavy use.

The best time to superchlorinate is after sundown, to avoid chlorine waste through dissipation by the sun's ultraviolet rays. You can do it at other times, but do not allow anyone to use the pool until the residual chlorine level drops back to normal (which, in most pools, is below 3.0 ppm). The product directions should give you the amount of time needed before you can safely use the pool again. If this information is not provided, ask a pool service company how long you have to wait before swimming can be allowed. If at any time between scheduled superchlorination treatments the chlorine residual drops to 0, the water should be superchlorinated promptly. A reading of 0 is often, in fact, below 0, which means that some chlorine demand has accumulated in the water, and bacteria and algae growth will develop rapidly. In hot weather a residual reading of 0 can turn the pool water cloudy and green within a day or two.

One word of caution: don't superchlorinate when the pH level is low (acid). If you do, any copper dissolved from the pool equipment or plumbing by the acidic water may be oxidised by the large dose of chlorine and cause black stains on the pool finish.