Quote Originally Posted by CarlD View Post
Chem_Geek can explain it to you better, but FC breaks down the CC. It takes about 7ppm of FC to eliminate 1ppm of CC (I THINK that's the ratio--Richard, correct me if I'm wrong). So you need to shock sufficiently to get rid of the CC.
The traditional industry rule is 10x, but technically that's really only for ammonia (which is measured in units 5x smaller than all types of chlorine including combined chlorine). For CC, the required amount is actually less than 1x, but you should shock with a higher FC to make it go faster. Shocking with chlorine at the shock level in Ben's Best Guess CYA chart will more quickly get rid of most CC. Keeping the pool uncovered and exposed to sunlight will also help.