Hi,

We put in a 20x40 liner pool at the end of August last season. We are in NE so in the same general area of the country as you. Our liner is 28mil all the way around. We have a Hayward DE filter and have been very happy so far. We have a lot of pine trees around us and the DE filter has done a great job keeping the water clean. We have the goldline (owned by Hayward I think) Aqualogic P4 SWG - and LOVE IT! We also have the Hayward colorlogic light and are very happy with that as well. We have a rectangle shape so one light was fine for us, but if you have a different shape, I would recommend more than one light.

As far as the bottom goes - we have a sand \ vermiculite mixture. We were told that it would be porous enough to let water through without causing sink holes or erosion like sand. I have read about problems with plain concrete \ sand where the bottom of the pool looks rough and even can spring holes because of rough concrete. The bottom of our pool is very smooth and is very even. At night when the light is on, it looks so smooth and level.

Good luck with your purchase!!!