If the level of free chlorine is too high, which chemical can be added to reduce this level?

Sodium Thiosulfate is commonly used as a dechlorinating agent to lower high levels of free chlorine in pool water. When added, it reacts with the chlorine to form chloride ions, thereby effectively reducing the chlorine concentration. This is particularly useful in situations where chlorine levels exceed recommended amounts, ensuring safe swimming conditions.

Other options, such as Sodium Hypochlorite and Soda Ash, are typically used to increase chlorine levels or correct pH, while Muriatic Acid is effective for lowering pH but does not address chlorine levels. Hence, Sodium Thiosulfate is the appropriate choice for specifically reducing high free chlorine levels in a pool.