Split from here: cya-chlorine-t37065.html
It is always best to start your own thread when you have a question. Butterfly
I'm having a similar issue with CYA. Although it was very high last year when we bought our house (May 2010), we went through the first summer on the BBB method and over time brought our CYA down to a desireable level. After the pool opening refill back in May 2011, large amounts of rainfall, and some refilling with the hose due to evaporation in the hot summer (plus normal splashout and a pesky drip now and again from the filter), the CYA now seems to be down somewhere below 20 (as tested by my TF-100 kit a few days ago. There's literally no amount of liquid that I add to that test tube that made the black dot fade out of sight). Granted it's been quite hot here in Chicago for the last few weeks, yesterday after work I added 2 of the "large" bottles of bleach from Wal-Mart and tested my FC in the morning. At that point, I was at about 11 or so (FC). After I got home from work today, I tested again and it was at MAYBE .5 (FC) if not 0. Under this, I'm spending $5/day on bleach and it's still not cutting it. I can only assume I need to raise my CYA, correct? Assuming my other levels are in check, what's the best way to approach this and, to what level should I bring it?