My 37gal All-Glass has a plastic strip that goes across the top in the center, similar to the brace on a 55. This strip is wide, thin plastic and it is very flexible, and has no tension whatsoever on it.
I have a strip light that I just got and it has an LED
moonlight that is right in the center, covered by this piece of plastic, so I want to cut the thing off so the LED
will shine into the tank. I don't know why it is there if not to add support, but it does not seem to require it. The tank is 30" wide, 23" tall and about 12" deep.