I have 2 tanks with 6' x 3' footprints that have 1/2" glass. One is a plywood tank with angle iron all around and two metal braces across the top (definitely no bowing there) and the other has a very large center brace and two side braces. I added braces along the front edge as well (for peace of mind). I think 1/2" is okay for 2' tall tanks if it is well braced.