We have a 13,500 gallon pool with spa, with all pentair equipment. We also have a UV Ozone system. The pool is almost 4 years old, it has a pebble tech finish, and we have two oak trees that drop leaves in the pool and it gets quite a bit of shade. I’ve always had pretty good luck keeping the pool chemically balanced, however this year my CYA keeps getting high (CYA got over 100, I drained half the pool and got it down to mid 50s, now I'm back up to 95) and I’ve made a point to use less chlorine tabs. I’m using 3 tabs a week compared to I use to fill the chlorination up the first year we had the pool. Also my PH keeps going up and alkalinity keep getting to low. I've never had this problem and we haven't changed any chemicals, I'm totally confused as to why this is happening. Any help would be appreciated. A couple of side notes, I still have the original cartridge filters and I just clean and reinstall. Also, the chlorinator seems to have a lot of residue in it now.