The ideal range for pH in swimming pool water is 7.0 – 7.6. The pH of eyes is typically 7.2 – 7.4. If the pH is kept at the same level as that in eyes, the side-effects of burning red eyes is kept to a minimum. The ability of chlorine to disinfect at this level is also optimal.
Lowering high pH in pool waterAdding an acid to the pool water reduces the pH level. The most common chemicals used to reduce high pool water pH level are:• Muriatic acid: Typically 30 – 35 per cent liquid hydrochloric acid• Sodium bisulphate: Granule or powder pH reducer, dry acid.Other acids that have been used in pool water are:• Sulphuric acid: Raises TDS levels and adds sulphates to the pool water• Nitric acid: Highly corrosive but is known to work well.
If the total alkalinity of the pool water is within the recommended parameters of 80 – 120 ppm, pH reducer should be added according to the instructions on the container. The acid should usually be added to water and mixed before dosing the pool. The pump should be running when the acid is slowly distributed around the pool. Low pH in swimming pool water may cause one or more of these following problems:• Eroding of the pool plaster or grouting• Corroding of the metal pool accessories (steps, heater, etc)• Staining resulting from metal corrosion• Rapid dissipation of chlorine requiring increased dosage• Burning eyes and nose• Dry, itchy skin and scalp• Perishing of swimwear, pool toys and accessories.
Raising low pH in pool waterAdding a base or alkali raises the pH of the pool water. If the total alkalinity is normal, pH increaser should be added according to the instructions on the container. The active ingredient is usually sodium carbonate. Often low pH is a result of acid rain and occurs after periods of heavy precipitation. The normal tendency of pool water pH is to rise through exposure to wind, sunshine and bathers. The most common cause of consistently low pH is low total alkalinity, which should always be adjusted (with sodium bicarbonate) before trying to increase the pH.