pH is a measure of the acidity or alkalinity of a solution. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are alkaline.

Total alkalinity measures the water’s ability to resist pH changes and is expressed as the equivalent amount of calcium carbonate in the water. If total alkalinity isn’t kept within the recommended range, adding more chlorine can cause the pH to drop too low, making the water acidic and unsafe.

The ideal total alkalinity level is between 80 and 200 mg/L. Because chlorination produces small amounts of acid, alkalinity must be maintained at all times to stop the water becoming acidic. This is usually done by adding soda ash to the pool water.