If the level of free chlorine is too high, which chemical can reduce it?

Sodium Thiosulfate is the correct choice for reducing high levels of free chlorine in pool water. This chemical acts as a chlorine neutralizer and is commonly used in pool maintenance when chlorine levels exceed recommended limits. When added to water, Sodium Thiosulfate reacts with free chlorine, effectively deactivating it and reducing the chlorine concentration to a safer level for swimmers and to prevent damage to pool surfaces and equipment.

In contrast, sodium hypochlorite is a form of chlorine itself, so it would not help in reducing chlorine levels. Soda ash, or sodium carbonate, is typically used for raising pH levels and does not impact chlorine concentration directly. Muriatic acid is mainly used for lowering pH and alkalinity but does not directly mitigate high chlorine levels either. Understanding these roles helps reinforce why Sodium Thiosulfate is specifically effective for this purpose.