To paraphrase
@bzb from a comment elsewhere, "I've built plywood-only speaker boxes that you could drive over with a truck. No 2x4's needed."
If the sides are built and joined well, this should be plenty. With a continuous edge support all the way around on a rimmed tank, force is transferred laterally to the corners/sides and then directly down.
You'd almost surely crack the bottom glass with uneven weight distribution (like stacking a ton of heavy stone directly in the middle of the tank) before that stand sags/bows in the middle.
If this were a rimless, flat-bottomed tank, it would be a different story, but the bottom glass on this one is as supported and braced as it needs to be, and the only real concern is full support along the bottom edges.