"J. Clarke" wrote:
....

If I read you correctly there are 9 2x8s supporting this tank, with the
2x8s being supported on the ends by 2x12s.

To use the sagulator to get an approximation of the sag in the 2x8s, you
would plug 1100 pounds as the weight,

My apologies I misread "gallons" as "pounds"--that should be 8800 pounds (1
gallon weighs 8 pounds to a good approximation--8.33 to be exact).

But the calculation is on each joist so the load/joist is only 1/9 (or
1/8 if one wants to discount an end and be a little more conservative)
so the weight to plug into the robot is roughly 1000 lb (or 1150 lb if
use 8 instead of 9).