Greeting everyone. First let me say thanks in advance for this great resource. I've been reading for the past week and have taken control of my pool back from the Pool Store.
The pool is 7 years old, 10k gallons pebble-tec surface with a DE filter and a Goldline T-15 cell SWCG. This time of year, at least for the past 5 years, I struggled with keeping chlorine in the pool. I realize now that I never would get all the organics out of the water, which would then consume all the chlorine the salt cell would produce. The typical process would be
1) take a sample to the pool store
2) they measure zero chlorine and tell me to shock
3) put salt system in "super chlorinate" and run overnight
4) water looks better
5) 3 or 4 days later, take a water sample back in and measure zero chlorine
6) repeat until October
I have come to the conclusion that my pool was never properly shocked, since I would never get the FC level high enough or keep it long enough to remove the organics. I have the FAS-DPD test kit (thanks tftestkits.net) and can now measure my FC properly. This past week I've been trying to measure levels above 5ppm by diluting the sample with distilled water and multiplying the result (believe it or not it worked within 2 or 3 ppm). I ran an overnight test last night and went from FC 8.5ppm CC 0.5ppm to FC 5.5ppm and CC 0.5ppm this morning. It looks like I'm not done shocking, so I added liquid to get back to 17ppm. Depending on which pool store you believe, my CYA is 40 or 60ppm.
Back to my original question. How much FC loss is normal during a sunny day in Florida? If I turn my salt cell off and start with 17ppm, at my CYA level, how much should be left in the evening?