sorry for the delay in getting back to this thread, sometimes work gets in the way! I think I'm ready to shock this pool to 12ppm FC given my CYA reading of 30ppm and wondered about my CH of 388. I have 25 lbs of 73% calcium hypochlorite and 50-75 pucks (93% strength but it's not cal-hypo) on hand and I'm out of bleach. I've been using bleach since last week to maintain my FC level but it's more cost effective to shock with the cal hypo since i have it on hand and it's only a month old. Should I be concerned about raising my CH levels too much if I use this cal-hypo until it's gone? I'd like to use what I have on hand if possible without suffering ill effects. I'll post my numbers this evening before I shock so we can monitor progress. on a side note, what levels of FC in the water are harmful to swim in?