My 21' above ground pool in northeast Ohio freezes each winter. There is 52" of water in it now and that is 3" below the wall caps. I usually don't have it this full, but we've had a LOT of rain lately. I was told to drain some water out of it so that the rising ice will not destroy the top pieces of the walls. How low from the top of the rails do I have to drain? I really don't like the idea of wasting water and then paying to fill it again in spring. But I also don't like the idea of buying new wall caps. As a related question, I usually put an "air pillow" under the winter cover because I was told this helps keep the expanding ice from pushing out against the walls. Is this bunk or a justified practice?