Pool water pH is a measure of how acidic or alkaline it is. The pH of a solution can range from 0 to 14. A pH of 7 is considered neutral, while a pH below 7 indicates an acidic solution, and a pH above 7 indicates an alkaline solution. The ideal pH range for pool water is between 7.0 and 7.4. Maintaining this range is crucial for several reasons.

pH affects the effectiveness of chlorine, which is a disinfectant used to kill harmful bacteria and viruses in pool water. Chlorine comes in different forms, but free chlorine is the most common type used in swimming pools. Free chlorine is a combination of hypochlorous acid (HOCl) and hypochlorite ion (OCl-). HOCl is the active form of chlorine that kills bacteria and viruses, while OCl- is a weaker form that can still disinfect but is less effective.

When the pH level rises above 7.8, the amount of HOCl produced is drastically decreased, making the chlorine less effective at killing harmful bacteria and viruses. This means that maintaining the pH level in the recommended range is critical to ensure that the chlorine can do its job effectively.

To ensure that the pH level remains within the ideal range, pool operators need to test the water regularly using a pH test kit. If the pH level is too high, the water can be corrected by adding an acid, such as sodium bisulphate. If the pH level is too low, the water can be corrected by adding an alkali, such as sodium carbonate.

To measure the free chlorine level in pool water, a DPD1 tablet test can be used. However, this test measures both HOCl and OCl-, and does not provide information on the active chlorine level. This is why testing for pH is just as important as testing for chlorine. Only when both levels are within the ideal range can swimmers enjoy clean and safe pool water.