I repeat thats not my tank its a example. And FYI ive seen hundreds of tanks with shells that havnt cracked. Its all about pressure and torque on that point

Yes which has nothing to due with the tank being level, if it's properly supported and the glass is ground flat or placed on the outside that type of failure won't happen even if you're out by an inch.

Out by a inch? If your tank is out by a inch it WILL break even if its perfectly made... Its just a matter of time...
Ive seen many broken tanks and even seen acrylic tanks that cracked being out of level

wrong, I can prove it with science.

If you're worried about it being closer to perfect, and for your 40b, I use the composite shims from home depot
These may be similar to what I used. Mine are man-made composite plastic and grey-ish
They don't crush like wood and are easy to score and snap

As for your leveling, my 125g was out 3/8" left to right and no worries for over a year
My 75g is perfect using the shims

Just keep in mind that you may want to re-level it after it's full and has settled for a day or 3

Im not wrong, Im a glazier I know how glass works and cracks when its torqued out of level.
But im not gonna continue to argue with you, thats not the point of this thread

How does one re-level a full tank?

I'll have a look for those shims.

I have always used plate steel for shims. Any metal shop can cut you some from scrapes.
When I leveled my 90g I filled it up 4" to level the water line cuz the plastic top might not be level right. I then shoved a small pry bar under it and lifted and slide the steel under. Filled it half way and checked again. Filled it just below rim and checked again. This winter I had to relevel my tank from the screwy winter we had. I just drained 10g off to see the water line and got my bro to use a small prybar under it so I could get a bigger one under the stand to lift it another 3/16" then put thicker steel shim in

Actually it is the point of the thread, to determine how much it matters for tank to be off level. That said I'm also glad you polish glass for living, I'm a professional stress engineer, I design tanks and vessels among other things and on top of that I even use to build aquariums.

The simple fact is if a tank is built and supported properly then there are no pressure points. The only stress is created from the pressure from the water and that doesn't change if the tank is not level, running a wave would have a much higher affect and even that isn't enough to over-stress a tank. These pressure points your talking about are result from uneven glass edges contacting one another, this will cause issues even if the tank is perfectly level. Also shimming a tank isn't a good idea, the stand should be shimmed and the tank receives even support. This is why foam is often used and recommended to provide even support the base of the tank. This is what is critical, not the level.

Woah, I didn't mean to imply the tank itself should be levelled, but instead the stand
I may have used the word 'tank' in general as a reference to the whole unit :smile:

Thanks for the clarity on this sphelps