I never really got my CYA all that high last year and we had so much junk floating in the pool when we opened this year, I didn't get it up to where I wanted it until a couple of weeks ago. Before that, and all last year, I had the intellichlor at 40% running about 8 hours a day. While last year I had no issues, the chlorine was a tad low so I just bumped it up to 10 hours and that seemed to get things back on track.
So, I got the CYA up to about 70-75 and I backed off the IC40 to 30%, still on 10 hours a day. I look down after a few days and the deep part is looking a tad cloudy. I check and I've got almost no chlorine and the CYA is down to 50. Taking the lazy route, I cranked the IC40 up for a few days and the water very quickly was back to being crystal clear. So, I figured maybe the CYA sucked up all the Chlorine and I needed extra to get back into balance, so I backed the IC40 back down to 40%. Whereas in the past that has been a good maintenance number, when I checked today, I have about 1.0 for Chlorine and what I'm guessing is less than 0.5 for CC (it was ever so slightly pink and went away with one drop).
My question is then why is that with no CYA, I ran perfect on 40%/8 hours last year, but this year with a full recommended dose of CYA and 40%/10 hours, I can barely keep ahead? What did I miss here and where did I lose a third of my CYA in the span of just a few days?