Which chemical compound is used to raise pH levels in water?

Sodium carbonate, often known as soda ash, is utilized to raise pH levels in water. Its alkaline properties allow it to neutralize acidic conditions, effectively increasing the pH. This adjustment is crucial in various applications, including pool maintenance, wastewater treatment, and industrial processes where water quality must be maintained within specific pH ranges.

The other options do not serve this purpose effectively. Sodium bisulfate is an acid that lowers pH. Muriatic acid, which is essentially hydrochloric acid, is also used to decrease pH levels. Calcium hypochlorite is primarily used as a disinfecting agent and can affect pH but is not intended for the sole purpose of raising pH levels. Thus, sodium carbonate is the appropriate choice for increasing pH in water.