I probably would have used 2x6's thought for that much water.
Definitely a great looking stand though.
With the braces in between each corner, what you have should work great.
An update!!! My Sump is now finished and my Reeflo pump and my TMC Pro UV 110 sterilizer are here (see pics below). Things are really starting to come together. More updates to follow as soon I as I get some free time from work