Which chemical is typically used to lower pH levels in swimming pools?

Muriatic acid, which is a strong acid composed primarily of hydrochloric acid, is commonly used to lower pH levels in swimming pools. When pH levels rise above the ideal range (typically between 7.2 and 7.8), muriatic acid helps to neutralize the alkalinity, effectively reducing the pH. This adjustment is essential for maintaining water chemistry, ensuring that chlorine is effective as a sanitizer, preventing scaling, and providing a comfortable swimming environment.

Sodium bicarbonate is used to raise pH and increase alkalinity, so it serves a different purpose in pool maintenance. An alkalinity increaser is designed to stabilize pH levels by increasing total alkalinity, not lowering it. Calcium hypochlorite is a chlorine product typically used for sanitation and disinfection, and it generally does not have a significant effect on pH levels. Thus, among these options, muriatic acid is the correct choice for reducing pH in swimming pools.