If calcium hardness is too high in pool water, which chemical should be added?

When dealing with high calcium hardness in pool water, the appropriate action is to drain water from the pool to lower its calcium levels. This option directly addresses the issue by reducing the total hardness of the water, as lowering the water level will also dilute the concentration of calcium in the pool.

While some chemicals like muriatic acid are effective for lowering pH and alkalinity, they do not directly reduce calcium hardness. Adding sodium bicarbonate will actually increase total alkalinity and, in certain circumstances, calcium hardness. Calcium chloride is used to raise calcium hardness levels, not lower them. Therefore, simply adding chemicals would not resolve the elevated calcium hardness issue.

In summary, the best approach for high calcium hardness is to remove some of the pool water and replace it with fresh water that has a lower hardness level. This method effectively manages the calcium hardness without introducing any additional complications or imbalances to the pool chemistry.