I know the norm is to use 2x4 but I don't like working with 2x4's and 2x3 are much straighter and easier work with and from a cosmetic viewpoint it conserves space better, it's only 1 inch difference. Some prefer the more is better method, I prefer the less is better approach. The stand will eventually hold an 8ft glass aquarium 96x24x24. I'm planning on having two tanks below it, maybe two 75's or two 120's. Would the vertical 2x3 hold the weight ? Does 1 inch really make a difference ? The weight would of course be distributed on wood not screws. Since 2x3 are less expensive, I could always add a few more extra vertical posts.