Thank you everyone for the wealth of information on this site yet again!
I have a 18 ' above ground Intex metal frame pool. I have had to continue using the filter that came with the pool, although I suspect it is smaller than is really needed. After fighting all last summer with algae, I closed the pool by just adding an extra bottle or 2 of bleach and lowering water below the filter intake. Then pulled the pump off and left the hoses and the rest attached. I did this in October/November time frame, as it does not get below 50 degrees much before then in Oklahoma. When I opened it this spring, I drained the rest of the water as is was a swamp, shop vac'd the clumps of yellow/brown algae from the bottom, filled, slammed. that worked as long as I kept the chlorine above 5, with cya 30 to 40. Of course, when I ran out of bleach before payday a couple times, it comes right back, so have been fighting algae still quite a bit this summer, but not swamplike. I am nervous about returning to full swamp conditions if I close it again this year. We typically have a few days to maybe a week at a time of below freezing weather, in a mild year it will warm up again the next day. The other option I see is to take it down completely, which I really am not looking forward to, and storage would be an issue if I had to do that.