I always wonder why some people have these problems. I have had my pool for about 9 years and never (am I just lucky?) have had any problems. I typically take the cover off the pool, drain the antifreeze out of the lines, start the pump and filter, shock the pool, turn the heater on and then go swimming. When I open the pool it is always crystal clear the way it was when I close it in the fall. Is this a function of my cover? I have a FOXX pool that has a vinyl cover much like a liner. There is a track above the liner and it locks into that just the way the liner does. It covers the pool so it is fairly airtight and nothing gets in it over the winter.