This is a great question that connects with something I've had on my mind lately.
In another thread (http://www.poolforum.com/pf2/showthread.php?t=4078) someone wondered when to allow Cl levels to return to normal. Their FC had dropped 1.5 ppm overnight but CC was registering <.5, and should shock be maintained until level all night. One respondent said they maintain shock levels until the water was clear. My understanding is that Cl doesn't really serve any purpose in clearing, only in killing off the baddies. Once that's done (CC<.5), it's served its purpose and the rest is up to the filter. And if that's not enough, a clarifier or other remediation should be considered.

So...

Can CC be used as THE indicator of a need for shocking, or allowing Cl to drop off to normal? It seems like it'd be more accurate than clarity or smell or whether the level sustained through the night and save on some Cl.

C.