Sorry to keep bothering everyone, but I am about to go crazy. As mentioned in my other posts, I am shocking my pool due to one reason: an overnight FCL of 1.5. Everything else is fine. But as I mentioned also, when I started shocking, I got a 4.5 drop in FC overnight. I thought that was weird enough, but today I have been pampering the pool trying to keep it at or above shock level, and now things are defying logic. I added bleach this morning and brought FC up to 22 (Shock level is 20 for my CYA). Two hours later, I was at 19. Okay, extreme sunlight loss, I assumed. I bumped it back up to 23 this time. ONE hour later I was at 19 again! Weird enough? Not yet: I bumped it back to 23, let it mix for about 30 minutes, and then decided to bump it higher so that I didn't fall below 20 again. I added half a gallon more bleach, waited 40 minutes; and I was at 22! Adding bleach brought it down! I thought maybe my titrating reagent was bad. I had another bottle, luckily, and retested; same result. I've tried getting water samples from different areas; same result. What the heck is going on!?