[Danny_Ocean]

You can level the bottom of the pool by filling with layer(s) of sand, wetting & compacting. Then those piers will have a chance at being level.

Additionally, I would tie the joists to the sides of the pool somehow, to keep them from twisting/folding in the event of a seismic event or over-load. Did/will you install blocking between the joists? Those long boards will twist and I doubt the attached decking will prevent that. In lieu of blocking, use some Simpson x-braces or seismic strapping across the top of the joists in an "X" pattern.