What chemical may be necessary if water hardness levels are too low?

Calcium chloride is essential for increasing water hardness when levels are too low. Water hardness is primarily determined by the concentration of calcium and magnesium ions; thus, when hardness is insufficient, it can lead to issues such as equipment corrosion and difficulty in maintaining proper water chemistry.

Calcium chloride serves as a direct source of calcium ions, which help to enhance water hardness. By adding calcium chloride, pool operators can effectively raise the hardness levels, ensuring the water remains balanced and protective of the pool surfaces and equipment. Maintaining appropriate hardness levels is critical in preventing damage and ensuring optimal swimming conditions.

Other choices like magnesium sulfate may contribute to water hardness but not as effectively for pool maintenance. Sodium bicarbonate primarily addresses alkalinity rather than hardness, while alum is used for sedimentation and clarification rather than hardness adjustment.