glass 3/16" 1/4"?

If you want a simple "can it be done?" answer, then YES! 3/16" is on the minimal side of safe, but I'm almost positive it would work fine for a tank that doesn't get much abuse (movement/banging/aggressive, large fish/etc.)

I will tell you that my Perfecto 55 gallon tank (approx 21" tall is made with 1/4" glass. It has been moved around quite a bit and housed roudy fish as well! I'd just be real careful about any "bumps" and maybe add a bit extra silicone in the corners. (because of slightly smaller jointing area).

I will also tell you that my new DIY tank I've just completed (5'x2'x2') is made with 1/2" plate glass. Some tanks this tall use 3/8" glass, but I tend to go on the "safer" side of things when I build. My stand is also comparatively "over-built".

Just before Christmas I bought a 29 Gallon tank measuring 30x12x18" or thereabouts. Anyways it was made with 3/16" glass and once it was completely filled with water it was bowed so badly in the middle (about an inch) I returned it immediately. I might have been ok but who wants to take a chance?

I just got a 55 gallon tank for free (used) and I measured the thickness of the glass. It's 3/8". Yes and with the thickness it is extremely heavy. It's sitting in pieces right now waiting to be resealed.

Although the 3/16" should be fine, the minimal cost increase by using 1/4" is a heck of alot cheaper than replacing the tank, floor, stand, etc etc. because of a failed glass pane.

Dont skimp on what is essentially the most vital part of any aquarium, the aquarium itself.