I'm assuming that the FC levels you show in your chart are residual before you add the "treatment" for that day? If so, what was the peak FC after the treatment?

I have a 29K gallon vinyl IG pool in full sun all day in Louisiana, and I find that if I don't keep my CYA levels pretty high, then I lose much if not all my chlorine over the course of the day. That's why you'll find posts of mine that refer to my ideal CYA, which is 80-90 ppm FOR MY POOL. (I would never recommend it that high for pools without similar circumstances to mine). So...although it's hard to say how much chlorine you're using up daily because I don't know what the peak was to begin with, if you think you're losing too much, you might try to "up" the CYA level JUST A LITTLE and see if that helps.

One reason that you'll find your chlorine levels fluctuate instead of staying steady like they did with the chlorinator, is that the chlorinator added a steady stream of chlorine as long as the pump was on....with bleach or cal-hypo, you need to add it as late in the evening as you can (after the sun is off the pool), to get as much sanitizing time out of the chlorine as possible--and make sure you put enough in to leave a residual by the next night.

Janet