If calcium hardness is too high in a pool, what should be added to lower it?

When calcium hardness levels in a pool are too high, one effective way to lower it is to use muriatic acid. Muriatic acid, which is a diluted form of hydrochloric acid, works by reducing the pH and alkalinity levels in the water, which can help to dissolve calcium deposits and lower the total hardness. When calcium becomes excessive, it can lead to scaling, cloudy water, and difficulty maintaining proper water chemistry.

It's crucial to apply muriatic acid carefully, and doing so directly over the main drain allows the acid to be efficiently mixed in the water, targeting areas where calcium buildup may be more concentrated. However, it is recommended to consult pool chemistry guidelines and safety instructions when using strong acids like muriatic acid for treatment.

The other options provided are not suitable for lowering calcium hardness. Sodium bicarbonate is typically used to raise alkalinity, while calcium chloride is added to increase calcium hardness. Not needing to add any chemicals would overlook the problem entirely and could lead to further complications in maintaining water chemistry.