There is a determination between "Free" Chlorine and "Total" Chlorine. Free Chlorine measures the chlorine that is still available to continue sanitizing, disinfecting, and oxidizing the pool water. Total Chlorine measures all chlorine in the water-Free Chlorine and the presence of Chloramines. It is necessary to separate Free Chlorine and the presence of Chloramines because Chloramines are so unsuccessful and undesired in the pool water.