Ammonia form CYA this year, but not years past?

[chem geek]

Good question and my gut feel is no, it's not a good idea unless you find some way to mix the water even if you don't do it using the regular pump. Perhaps using some sort of submersible pump temporarily after adding the chlorine might mix it up somewhat if the pool is small and you point the outlet hose in a way that tends to swirl the water (especially for a round pool).

Closing late and opening early is probably your best bet. Some people close with a strong dose of Polyquat 60 in addition to chlorine. If the water is cold enough, the Polyquat will last quite a while. Even chlorine will last if not exposed to sunlight. In my own pool with a mostly opaque cover and with the water at 50ºF during the winter, my daily chlorine loss is around 0.1 ppm FC, but I'm able to maintain the chlorine level adding some every couple of weeks.

[CarlD]

Richard's right. I close by waiting till the water is 60 deg or less (if practical), shocking my pool up to the CYA shock level, adding 1 quart of Polyquat, waiting 48 hours (Polyquat drops FC levels), bringing it back up to shock level, and closing. I use a safety mesh cover. If we have a good, cold winter I'll get a foot of ice on the pool. By mid-April, when the ice melts, if I open then, I usually do NOT have algae. I've only had algae the last two openings--because I opened late last year and this winter was warm. But it was cleaned up very quickly because I don't hesitate to hammer it with LC, usually in 24 hours.