+1 what JJRocks said. I'm in the same general area as JJRocks and have been pool stored by seemingly helpful people, who actually know less than untrained monkeys (sorry about insulting the monkeys). So cavaet emptor , get a TF test kit to control your destiny, and a magnetic stirrer to make your life easier.
My brother has a vinyl pool and has left his open, similar to JJ, for about ten years with no freezing problems. He just likes the view and claims the work and money is about the same either way.
Like I said, mine is winterized. I have a safety cover and keep the water at least an inch below the tile. I dunno if the water level matters, but it is what I do. I close mine because I have a cover, I hate the leaves and want to minimize the pollen mess....but some leaves, bugs and pollen get under the cover. The dog thinks the cover is her personal sunning bed and short-cut, so I guess that is a benefit.
I have a 1969, 20 X 40 plaster; 36K with swg. I love my Nitro robot (or whatever it is) which seems to eat oak leaves without a problem.