Bottom pane of glass thinner than the others?

[Quo Vadis]

I am about to put up my 155g tank (48"x24"x31") that I just resealed and I realized (when I was super gluing a crack on the bottom plastic frame), that the bottom pane of glass is much thinner than the rest of the glass. The glass on the sides is 5/8ths glass, but the bottom glass is only 1/4th inch glass. I hadn't been able to see this before because the frame was covering it. Is this normal on big tanks, or should I be worried?

 

[DMD123]

Most likely they used tempered glass. A lot of times on the tank they have a little sticker on it that tells you not to drill because it is tempered. But with an older tank may have come off.

 

[Quo Vadis]

Yes that was my guess, but I was just surprised by the difference in thickness, since the bottom was less than half as thick as the rest of the glass.