I haven't used my pool much in the past month (just used the spa once). I'm just getting ready to close it for winter. The cover has been on for a month or so.
The last time I tested calcium hardness was Sept. 28th and it measured 260. Today I am testing it and the reading is zero! I have a couple different bottles of the first reagent you are supposed to use (which would cause a red color) and they are both showing the same thing. I also sampled water from a few different areas of the pool and let things circulate for a while but nothing changed.
My free chlorine is 8, alk. is 110 and PH is 7.9. I was running my filter and SWG some each day just to move things around because some nights have been below freezing.
Any ideas what might be causing this? The water is cold but I've tested it this cold before and did not have this problem.