Combined chlorine (CC)
Also called: CC, chloramines.
Combined chlorine (CC), also called chloramines, is chlorine that has already reacted with sweat, sunscreen, oils and other contaminants and been used up. The target for combined chlorine is 0, a reading of 0.5 or below is acceptable, and above 0.5 it is time to SLAM the pool.
Why it matters
Chloramines are what smell like chlorine and what burn your eyes. They build up when there is not enough free chlorine to break through them, so a strong pool smell means too little free chlorine, not too much. A properly chlorinated pool barely smells at all. Combined chlorine is not a reading of its own. It is the difference between the free chlorine and total chlorine readings, so a small error in either one lands entirely in the CC number. A strip cannot resolve that. A FAS-DPD drop kit can.
In numbers
A CC of 0.4 versus 0.6 is the difference between "you're fine" and "SLAM the pool."