Leveling tank from uneven floor

[gregzz4]

Can you do anything from below ... Jack posts maybe?
Or at the very least have a look at the floor joists to see if they will handle the weight. If they are weak, shimming will only be a temporary solution as they will continue to deflect to the center of the room over time.

Mine in one area are cracked so I temporarily used a jack post and 2x10s to brace a few of them while a tank was in that area (temp spare tank)