Test the water to determine its current pH. The ideal pH range is between 7.0 and 7.6.
The acids used to reduce pool pH include muriatic acid, granular sodium bisulfate, nitric acid and sulfuric acid. Muriatic acid and sodium bisulfate are the most popular choices because they are powerful but rarely damage pools and filter systems.
Consult the acid container for mixing information. Fill a large bucket with water, and bring it to the pool area. Activate the pump, and then add the acid to the bucket. Do not add more than the manufacturer recommends.
Slowly pour the acid mixture into the water as you walk around the perimeter of the pool.
Wait several hours and then retest the water. Add a more diluted acid if the pH is still too high.
Test the water frequently, and adjust its pH as soon as you notice a problem. This protects the pool and its users from drastic chemical changes.