Liquid (muriatic acid) or dry granular (sodium bisulfate) substance used to lower the pool's pH (toward a more acidic condition) or to lower total alkalinity levels.
The amount of acid required to lower the pH and total alkalinity of pool water to the correct level. A titration test is used to determine proper amounts of acid (or pH decreaser) to reach correct levels. For example, to lower pH from 8.0 to 7.6, your pool may demand 2qts. of acid.