I'm guessing your mesh cover is the influencing factor here...I'm about 30 miles south of B'ham, and for the four years I've had my pool, I don't close, just cover with a solid cover. For the past month I've just been running the filter for about an hour a day to keep it circulated, and then for the handful of times we drop below freezing I let the pump run all night then turn off on way to work in a.m. as it never stays below freezing during the day. No sense for me to go to all that work of closing. Of course I would be in tough shape if we had a prolonged power outage AND the temps dropped below freezing.

If I don't feel like peeling a few waterbags off to get a water sample periodically (although I rarely do as my chlorine level stays stable until I uncover in May because the pool gets no sunlight), after running the pump for the afternoon I'll turn it off then take a sample from the secondary basket at the filter location. There should be no difference between this water sample and what's literally in the pool at any given moment -