When it was being built, they put something in that the builder called "Pool-Lite". He described it as concrete mixed with vermiculite. So it's like these little styrofoam beads in a cement mixture. The walls also have a blue padding about 1/8 inch thick to pad between the wood wall and the vinyl.

I was not around when they poured, so I'm not sure how thick the pool-lite is on the bottom. And unfortunatley the pool builder has gone out of business (maybe because of poor workmanship?).

I know the deck around the pool is four inches thick, and we have had some problems with it settling since it was built seven years ago. We even had to replace a section of the deck the second year. I don't think the ground was properly tamped before they poured the deck. Could they have cut corners on the pool itself? I can't imagine the pool settling so much that it leaves a gap this large in the concrete.

My pool is in west central Georgia. My cousin's pool in south central Alabama was built about 30 years ago and it seems to have sand below the vinyl. You can feel it give under your feet when you walk in their pool. Maybe the code was different back then?

I was thinking that maybe something like a caulk gun could inject some material through the hole in the liner to fill the void under there. Any suggestions on what that material should be? This is starting to bother me.