j walker wrote:

I think that I use the term "beam" in a different manner.

What you mean? Different from what?

I call a floor joist a beam and apparently that is incorrect.

Why you think that? It functions that way, a "joist" is a specific use.

This clarifies one thing; why the sagulator refers to a beam "standing
on end."

A beam "standing on end" is a column.

So, how do I get the sag in a floor joist?

I plugged in 1100 gal * 62.3 lb/ft^3 * 0.1337 lb/gal / 9 joists == 1020
lb load per joist. Putting in a span of 96", height of 7.5 and depth of
1.5 for an tuba8 and a long-leaf pine (SYP) for specie I got a
deflection of roughly 0.1". For a 2x10 it was closer to 0.05.

Depending on your actual orientation/layout, it might be better to
consider the load distributed on 8 instead of 9 intermediate joists.
That'd raise the load by 9/8 and increase the deflection to 0.15",
roughly for the 2x8.

HTH...

BTW, seems reasonable altho I didn't hand check the calcs returned by
the robot...

What you need to make sure of (at a bare minimum) is that you've got
adequate structural connection details throughout the entire
structure, including whatever the 2x12's of which you speak are resting
upon and what their span/spacing is to ensure they have enough
additional loading bearing capacity.