Were you using pucks in the past and bleach this year? That will do it. Pucks drop your pH while bleach raises it. That is why I use half pucks and half bleach, then I never have to mess with my pH by added separate chemicals. When it is low I use bleach, when it is high I use pucks. I don't worry about CYA going up as water naturally gets lost due to backwashing or on weeks like this where I got 7" of rain and had to pump out that much water.