Does winter (midwest) impact CYA levels?

Again, I echo watermom. I do drain below the skimmer but that amount of draining and refilling would not significantly reduce a CYA of 40-50. I've always ***umed there was some dilution of water through the ever increasing small holes in my winter cover. I check the chlorine level and for CYA before I even start raising the water level, because that helps me figure out how many tri-chlor pucks to start with for my CYA. Most often the CYA barely registers (20 or far less) and this year there was absolutely no measurable CYA at all.

For Richard:

Yes I cover the pool, usually in mid-October. And since, by mid-October most of our leaves are IN the pool... that means I have to skim, vacuum and shock before we cover.

Some years our pool freezes solid by Christmas, and other years it doesn't hit that mark until mid-January. Generally it starts to seriously thaw in March, and we usually open in May. Spring of 2005 we had a heat wave and opened in Mid April.

Jean