To lower pH levels in a pool, which of the following should be used?

Sodium bisulfate is a commonly used chemical for lowering pH levels in pool water. It is an acid that, when introduced to the water, reacts to decrease the pH level, creating a more balanced chemical environment. Maintaining the appropriate pH level is crucial for effective disinfection and can enhance swimmer comfort, since high pH levels can lead to eye irritation and scaling on pool surfaces.

The other options do not serve the purpose of lowering pH. Calcium carbonate, for instance, is primarily used to raise pH and stabilize water hardness, making it unsuitable for this function. Chlorine tablets are disinfectants that help manage germs and algae but do not directly affect pH levels significantly. Algaecides are primarily used to control algae growth and do not play a role in adjusting pH levels. Therefore, sodium bisulfate is the correct choice when the objective is to lower the pH in pool water effectively.