All chlorine based sanitisers become less effective at killing bacteria and viruses as pH rises ( Become more alkaline)
To keep the chlorine working it is recommended that pH is kept below 7.6. However if pool water becomes less alkaline it also gets corrosive and less comfortable to swim in. Also if pH drops below 7.2 it will start to attack some liners. Therefore the pH is recommended to be above 7.2. So the normal range that a pool water should be kept at 7.2 to 7.6 (Ideally7.4 to 7.6 ). On most pools the pH will tend to rise so pH reducing chemicals like sodium bisulphate is added .
swimming pool pH