Free chlorine is the measure ...
Published by Dennis McBride, Sr. Water and Wastewater Treatment Consultant at Burns & McDonnell
Free chlorine is the measure of the amount of hypochlorous acid (HOCl) formed by the addition of chlorine to water. Combined chlorine is the measure of the amount of chloramines formed when chlorine is added to water containing ammonia. Total chlorine is the sum of the free + combined chlorine.