Sand has a nasty habit of moving - I wouldn't recommend it. What I'd use -- if you can get it -- is what the limestone quarries here (limestone areas of N. Georgia and middle Tennessee) call "crusher run". It's mix of particles from fines up to sharp 1/2" stones, and compacts well.

Out of level (depressed) in the MIDDLE of the pool by 1 - 2" is not an issue. The issue is side to side.