Cool stuff.
You could always double-up a 2x6 or 2x8 in behind the front beam maybe if you wanted to keep the area brace free.. I built the stand for my 280g using a 2x6 and a 2x8 doubled up to cover the span and when I had water in the tank I measured for any signs of deflection and could not find anything even after 2 months. I'm not a structural engineer though so I'm not sure if there's a better criteria.