I'll run some calculations for you seeing that I am an engineer
But I need some more information.
1. under this location what type of beam is it? most likely an I beam. If it is, give me the dimensions, (length, width and thickness)
2. The distance from each edge of the tank to the nearest post
( ||<------------->| TANK |<---------------|| )
the || are posts
3. What is the size of your floor joists? 2 x ?
with this information, I can tell you what to do to keep your walls from cracking and your joists from bending too much.