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POOL PLANT – UNDERSTANDING PH pH – The Most Important Parameter?


RICHARD LAMBURN, STA’S POOL PLANT TECHNICAL OFFICER TAKES A CLOSER LOOK AT PH – WHAT IT IS, WHY IT’S ESSENTIAL TO MEASURE IT AND THE CONSEQUENCES OF HAVING WATER WITH INCORRECT PH


WHAT IS PH?


pH readings are set on a logarithmic scale ranging from zero to fourteen. A logarithmic scale results in a pH reading of 5 having 10 times more hydrogen ions than a pH of 6. Moving from a pH of 5 to 6 doesn’t sound that much, however in reality the composition of that water changes substantially. pH is the power of hydrogen within the


water. Water can be acidic, alkali or natural according to the ion content. Water also known as H²


O is made up of


two hydrogen atoms and an oxygen atom. If we break this down a little further we get two ions; the Hydrogen Ion (H+) and the Hydroxyl Ion (OH-).


The Hydrogen ion is acidic, whereas the Hydroxyl Ion is alkali. Therefore whether a solution is acid or alkali depends on the ratio of these two different ions.


If water has equal quantities of these Ions then we get a neutral pH, which would be 7. The level of pH is dependent on the concentration of these Ions in a solution or our pool and spa water.


This pH reading therefore determines whether a substance is neutral acid or alkaline.


WHY MEASURE PH? BATHER COMFORT:


pH hugely affects the comfort of bathers within the pool or spa, bearing in mind the pH of eye fluid is approximately 7.5 and fluctuations away from this pH can have a radical effect on the eye and therefore bather comfort. If the pH was to fall below 6, then the acidic solution has the potential to dissolve teeth.


The skin also becomes very sensitive when the pH drifts above 8 and below 7. If the pH goes above 8 then there is a potential for the lipids on the skin to be broken down, leaving the hair follicles open to infection.


MAINTENANCE:


If the water becomes acidic (below a pH of 7) then corrosion can occur on plant room equipment, pool tank grout, tiles and screed which can be costly. At low pH, water can even dissolve copper/metal pipe work and metal pump parts.


When the pH starts to rise above 8 then the water can transform to scale forming where lime scale is likely to accumulate, and potentially cause blockages, especially in


as possible.


The percentage uptake of these two chemical compounds is dependable on the pH of the pool water. The graph here details the effective pH on the percentage production of the Hypochlorous Acid and the Hypochlorite Ion. As the graph


demonstrates, at a pH of 8.0 only 20% of the chlorine is in the effective form of Hypochlorous Acid. The further down


“PH IS THE POWER OF HYDROGEN WITHIN THE WATER. WATER CAN BE ACIDIC, ALKALI OR NATURAL ACCORDING TO THE ION CONTENT”


42 June 2014 SPN www.swimmingpoolnews.co.uk


equipment such as heat exchangers. It is interesting to note that under corrosive conditions, calcium can be leached out of grout and appear as deposition. Sometimes this is misinterpreted as deposition, whereas it is the opposite.


pH therefore has a critical role in ensuring the water in our facility does not become excessively corrosive or scale forming.


FLOCCULATION:


Most coagulants work best at pH 7.3-7.4. Altering the pH will change the distribution of electrical charges. The pH can also have a strong effect on the degree of hydrolysis of the coagulant, which will affect its performance.


EFFECTIVENESS OF CHLORINE: Free chlorine, which is measured via the undertaking of a DPD1 test, is broken down to the two forms of chlorine that co-exist – Hypochlorous Acid and Hypochlorite Ion. These two compounds are what make up our free chlorine; the Hypochlorous Acid is the very effective sanitiser, whereas the Hypochlorite Ion is the weak disinfectant. To break down and eliminate the threat of bacteria we want as much Hypochlorous Acid


our pH, the higher the production of the Hypochlorous Acid.


Therefore it is essential not to allow our pH reading to go above 8, and to keep it within the recommended range. Without managing pH our chlorine can become ineffective at killing bacteria and ensuring safe bathing water is provided.


WHAT PH DO WE WANT? This information leads us on to a recommended pH of 7.2-7.6, with hard water areas accepting a pH up to 7.8, however, where possible the former is strongly recommended.


All the above factors make it imperative to ensure that pH is managed and within parameters. This ensures bather comfort, effective flocculation and maintenance, as well as chlorine residual that has the capability to control bacteria within the pool effectively.


In a future article we will look at the methods that will control the pH within the recommended levels and control our water balance.


STA 01922 645097 www.sta.co.uk


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