We opened the pool last week and I did an initial test using the Taylor 2006. I had no discernible CYA reading (filled the tube to the top and had no problem seeing the black dot). I finished last fall with a CYA in the 30s. Is it possible that the accumulated rainfall over the winter and spring diluted the water that much? We have a hole in our winter cover so we do take on some water during the winter.
I don't think this is the first winter that the CYA has dissipated. We purchased our house from someone who used tri-chlor as far as I know (he left quite a bit behind). Yet, I still needed to add CYA last spring as I was pretty low. I ended up adding enough CYA to raise the level to about 40-45 ppm. And I stiil finished the summer with less than that after the various rainfalls and splash outs.