Here's what I built for my 280. Notice the how the vertical 4x4's are cut so the weight supported by the 2x6's is transfered directly to the vertical supports rather than being supported by nails or screws.
I also sheathed three sides with plywood to prevent any lateral movement from the water sloshing around.
It wasn't very hard to build, and I'm confident it will hold the weight of the tank, water, etc. I personally wouldn't trust that much water and weight on a questionable stand. Not worth the risk, IMO.
mine is similar to the above picture just with 2x4's doubled and tongue and grooved and 8 verticals for my 180 my stand is definitely over build but i feel far safer