The metal frame is going to be very important. I don't know about
thickness. Might approach that with a glass company when you figure the
force at the center of the span. Your 3 x 3 x 6 is 54 cubic feet of
water, At 62.4 pounds per cubic foot, you have 3369.6 pounds of water.
You will need to be very sure of the base for your 1.68 ton tank!

We build a 94" x 9" x 15" tank out of window glass. To prevent
breakage, we have angle bracing along the bottom and top edges (bedded
on silicone) and have 3 cross pieces of aluminum across the top to take
the weight. In effect, we have four 23" tanks side by side. The volume
is relatively low as the tank is not very wide. Your 72" side will have
a LOT of weight in the middle.

JIM

Joe wrote:
Hi, I am trying to build a fish tank and am would like to have some
help and advices on it. The surface is going to be 6x3x3, my questions
whats the thickness of the glass i have to get to withstand the water
pressure? and whats the appro. gallon of water this tank can hold.
Thanks in advance.

Joe