Cool site for building a stand... does drawings for you...

[BCOrchidGuy]

I just tried it again for a 45 gallon tank, says the same thing, 4x4 lumber.

Remember if your tank is 48 inches long the plastic frame adds another 1/2 inch so that extra inch gives you a little extra.

FWIW I've got my 90 on a 1x4 frame with a center brace front and back, I built a 2x6 frame for it but I didn't like the height, the 1x4 frame was free so I used that. When I get my large tank... 150-175, I will use 2x4 and 3/4inch ply.