When I closed my SWG pool last October, my CYA level was between 60-70. I opened it yesterday and began the SLAM process, but my CYA test was not showing any at all! I filled the tube all the way and still clear. There was some rainfall and pumping done occassionally over the winter but I wouldnt expect it to have that big of an impact. How much of a drop is normal and where else could it have gone? I ordered some more CYA reagent in case that is it, but the bottle I have was pretty new, stored in the basement, and expiration date is in 2020.