if you're really worried about it, just build it like a huge window opening..... make a header for the front with 2 by 6's and make sure you have plenty of supports for this on each side of the header since you will not have center supports. if you are using a glass tank for the top, you should be fine. glass tanks only need support on the 4 corners really. if you build the stand with 2 by 6 joists going across, especially with the header idea i gave you, your stand will definitely support anything that fits on it