The sum of ซีแอล2, NaซีแอลO, ก.อ.(ซีแอลO)2, HซีแอลO and ซีแอลO– is called free chlorine (FAC) or residual residual chlorine (FRC), and is expressed in mg/Lซีแอล2.
At pH=7.5 (25°C, TDS=40mg/L), only 50% of residual chlorine exists as HซีแอลO, but at pH=6.5, 90% is HซีแอลO.
สัดส่วนของ HซีแอลO ยังเพิ่มขึ้นตามอุณหภูมิที่ลดลง. At 5°C, the molecular fraction of HซีแอลO is 62% (pH=7.5, TDS=40mg/L). In high salinity water, the proportion of HซีแอลO is very small (when pH=7.5, 25°C, 40000mg/L TDS, the ratio is about 30%).