Quote Originally Posted by iwannapool View Post
How often would I see CL, CC or FC, above 15 ppm? I guess if you get a big problem CC could go high, but FC?
If CC is over 15ppm you have a problem. But FC as high as 25? Sure.

If your stabilizer level (CYA) is over 100, you have to shock by getting FC up to 25ppm. You maintain your pool at something like 12-15ppm (I've forgotten exactly).

Unless you have very low CYA (20 or less) you normally will shock to 15ppm of FC--that's now at the limit of standard DPD kits. Past 15ppm ordinary DPD can bleach out and look like 0 ppm! Use FAS-DPD and you have lots of headroom.