pHlocrite for pH and Alkalinity Control in Swimming Pool Water - Water and Wastewater - Swimming Pools
Since 1982 when ICI Ltd withdrew chlorine gas for use in swimming pools, sodium and calcium hypochlorite have been used by most municipal pools for the disinfection of the water and, since both of these disinfectants are alkaline, acid is used to reduce the pH to the optimum value for pool water. A few public pools still use chlorine gas or liquid bromine and many smaller pools such as school and hotel pools use trichloro-isocyanurates for disinfection. All of these disinfectants are acidic when dissolved in water and require an alkali to maintain the pH in the correct range.
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When chlorine gas dissolves in water, it hydrolyzes forming hydrochloric acid HCl and the weaker hypochlorous acid, HOCl.
Cl2 + H2O HCl + HOCl
The acid from the continuous addition of chlorine gas to the pool water reacts with the alkalinity and is chemically transformed to CO2 and chloride.
2HCl + CaHCO3 CaCl2 + H2O + CO2
This equation demonstrates that the decrease of alkalinity and pH is not only a function of chlorine gas but of all chemicals releasing hydrogen ions in water, e.g. the commonly used flocculant aluminium sulphate. Trichloro-isocyanurate releases HOCl and necessitates pH and alkalinity control, although, due to lower bather load and thus lower chlorine input, the effect is not as signifcant as in heavily loaded public pools.
The effect of chlorine gas on alkalinity and pH becomes conslderable when the initial alkalinity of the make-up water is lower than 200 ppm as CaCO3 (4 meq/l). Hence, pH control is of great importance in order to ensure the efficiency of the chlorine residual and the prevention of corrosion of all materials coming into contact with such an aggressive water.
pHlocrite™ features two advantages over other chemicals used for pH and alkalinity control (sodium carbonate, sodium hydrogen carbonate) automatic control of pH and alkalinity. Without any electronic measuring device, the pool water is kept well balanced.
SI = O ± 0.5
No problems with cloudy water due to improper dosing of soda ash or bicarbonate, improves removal of iron and or manganese possibly present in the make-up water.
pHlocrite™ is usually placed as a thin layer on top of the sand layer inside any conventional sand filter (gravity or pressure type). In respect to the necessary freeboard, a portion of the filter sand can be substituted without diminishing the efficiency of the filter, as pHlocrite™ is superior to sand due to the roughness of its grains.