I am using a combination of bleach (8.25% from WalMart) and 3" pucks from Costco in a Frog feeder. I have an approximately 20,000 gallon IG vinyl pool. Using the Taylor test kit, my pH is consistently around 7.0 to 7.2 (seems like I've poured a lot of Borax into the skimmer this summer) and my Alk is consistent at 90 ppm. I know my CYA is probably off the charts because I have been using the 3" pucks for years (I tested recently and it measured around 100 ppm). However, water is clear and beautiful.

My issue is maintaining chlorine levels. If I pour an entire jug of the bleach in on one day (keeping the 3" pucks in the feeder), my FC levels are very low the next day. Example, yesterday I measured 2.8 ppm and this afternoon around 1 p.m., I get 0 FC reading. I read somewhere once that if you find the FC reading is below 0.5 you should immediately shock the pool but that would take a boat load of bleach (which is hard to come by in rural VT) and I hesitate to use the 1 lb. bags of "shock" because I know that adds more CYA. Since the water looks beautiful, I don't want to take any steps which are overkill (not ready to drain to reduce CYA) but I'd like to be able to keep FC of at least 1 ppm without having to pour in an entire jug of bleach on a daily basis.

I heard from our friend, a pool installer/servicer, that he's heard a lot of complaints this summer of people who can't keep a FC reading. I also had a new VS pump installed that runs more hours of the day at a lower RPM but this problem pre-dates the new pump.

Any suggestions on what could be causing my inability to get the FC higher with just the pucks? Or if I should do something different?