This can be just as important as having chlorine in the pool at all. The pH level in your pool should be about the same as the pH level of human tears, 7.2, though in the range of 7.2 – 7.6 is optimal. Chlorine is about 10 times more effective at sanitizing your water when the pH is at 7.2 rather than at a high ph level of say 8.2. pH can best be measured with a drop-type test kit versus a test strip, which can be easily misread.
Most often you’ll find the pH level is high; the best way to lower pH is by slowly pouring “Muriatic Acid” (AKA Hydrochloric acid) directly into the deep end of the pool while the pool pump is on and the water is circulating. However, granular acid (pH Minus or Decreaser) is safer to use alternative than Muriatic Acid.
When adjusting pH, add smaller amounts then retest after about 6 hours of continuous filtration. Readjust as needed. This will prevent “bouncing”. If you have a true pH bounce problem, that is typically due to a LOW Total Alkalinity issue; once properly adjusted, the pH should maintain itself well over a period of 1 to 3 weeks depending on rain, use, etc.
If swimmers are having a problem with “burning eyes,” high or low pH is probably to blame, not high chlorine.