What is a possible cause of low chlorine residual if dosing is correct?

Low chlorine residual can occur when there is an excess of ammonia in the water. This is primarily due to the formation of chloramines, which are less effective as disinfectants compared to free chlorine. When chlorine is added to water containing high levels of ammonia, a reaction occurs where chlorine combines with ammonia to form monochloramine or dichloramine. These chloramines do not provide the same level of disinfection as free chlorine and can result in lower total chlorine residuals.

While nitrites, phosphates, and nitrates may affect water quality and treatment processes, they do not directly lead to the same depletion of chlorine residual as ammonia does. Therefore, an abundance of ammonia is the most relevant contributor to a decrease in chlorine residual, making the relationship between ammonia levels and chlorine effectiveness critical for maintaining proper disinfection in wastewater treatment processes.