I am trying to include an ascii-esque diagram with measurements, but the font is being translated weirdly. Still, here it is. The numbers are where I used a dowl to take a 'pole' reading of the height of the water at eight different points within the tank. I took a 'reading' of the water height at eight points, starting near the back-right corner, proceeding in an order shown here:
back of tank
------------------------------
| 7 5 3 1 |
| |
| 8 6 4 2 |
------------------------------
front

1 - 15 14/16 (i.e. 15 7/8)
2 - 15 14/16
3 - 15 14/16
4 - 15 14/16
5 - 15 13/16
6 - 15 13/16
7 - 15 12/16 (i.e. 15 3/4)
8 - 15 12/16

So, it seems to me that front-to-back is level, it is only on the left side that it is 1/8" low. If I understand this, it means the shimming on the left side needs to be raised. I don't think the tank is being torqued; just squarely tilted, if that makes any sense.
I do have a 3 foot Calfo installed across the back of the tank, so the levelling issue you refer to re: the overflow is probably going to be a factor if left as-is.
Based on this comment of yours:
Quote Originally Posted by Instar
A 3mm tilt won't break the tank so long as its an even square stand support on all sides but level is always better. 3mm will affect the overflow to the sump if there is one.
sounds like it'll be better in the long run to drain, shim up the left side 1/8", then refill.
Thanks, Karl