Does winter (midwest) impact CYA levels?

[chem geek]

I believe the process Dave was referring to is that there are certain anaerobic bacteria (that is, bacteria that do not need oxygen to survive) that actually consume CYA. In fact, CYA is considered to be somewhat bio-degradable in the environment (soil) for this reason.

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). Many users of this forum do seem to startup their pool in the spring looking pretty full of algae and they just shock it to clean it up.

So your options are either to drain and refill (a certain way to reduce CYA) and keep your pool "clean" during closing by adding lots of chlorine, or don't add any chlorine during closing and "hope" that the CYA gets consumed. It's possible that even adding chlorine at the start of closing won't be enough to keep your pool clean as it the chlorine could get consumed over the winter season (this depends on what goes on in your closed pool over the winter).

Richard