finally starting the 54x54x21

[wheatgerm]

i have been wanting to get a 55g or 75g and build me a 4 foot square tank with 2 viewing windows.. it will actually be a little bigger than 4 foot giving me 2 to 3 inches to overlap the glass.. the tank will probably be about 25 inches tall but the water level wont be over 20 or 21 inches.. should be about 255gallons give or take right?? i would imagine the glass should hold just fine because i wont be adding any height.. only depth front to back? i think i have seen one other build like this on here but cant find it now. let me know what you all think and if you think the glass from a 55 will be strong enough to support 200gal plus as long as i dont go over 20 inches high