Quote Originally Posted by chem geek

However, if you "properly" close your pool by adding a large amount of chlorine to it, then the bacteria that consume CYA will not survive the chlorine. On the other hand, if you "let your pool water go South" by not adding chlorine to it, then you may get the sort of bacteria in your pool that consume CYA so that when you open up in the spring your CYA levels may be lower (but your pool will likely be full of green algae and need a lot of cleanup).
Then there are some of us who do close properly and who open to clear pools, (not green, no algae) and yet still have lost all the cya from their pool over the winter.