In a DPD test, what does a flash of pink followed by clear indicate?

In a DPD test, a flash of pink followed by a clear solution signifies the presence of chlorine. Initially, the pink hue indicates that chlorine is present at a corresponding level when the DPD reagent reacts with free chlorine in the water sample. If the solution then clears, it suggests that the concentration of chlorine is exceedingly high to the point where it exceeds the measurable range of the test. Therefore, the correct interpretation is that the chlorine residual is very high.

Understanding this process is crucial for aquatic facility operators, as accurate chlorine levels are vital for maintaining water quality and safety. High chlorine levels need to be managed appropriately to prevent harmful effects on swimmers and equipment. Ensuring that chlorine levels are within the ideal range is a critical aspect of water treatment and facility maintenance.