To increase alkalinity levels in pool water, which chemical should be added?

Sodium bicarbonate is the correct choice for increasing alkalinity levels in pool water. It acts as a buffering agent, which helps stabilize the pH level and maintain the overall balance of the water chemistry. By adding sodium bicarbonate, you can effectively raise the total alkalinity in the pool without significantly altering the pH level, making it a preferred choice for pool operators aiming to ensure a stable and comfortable swimming environment.

In contrast, muriatic acid is used to lower both pH and alkalinity levels, sodium thiosulfate is primarily employed for dechlorination, and hydrogen peroxide typically serves as an oxidizer rather than a pH or alkalinity adjuster. Therefore, these other chemicals do not contribute positively to increasing alkalinity and are utilized for different purposes in pool maintenance.