Nice tank, I have the same tank and stand, i love it.
I would drain some of that water from your sump, when i turned off my pumps for the 1st water change i was amazed how much water drained back from the overflows, i had to turn them back on drain some water from the sump and then shut everything back down for the water change.
Good Luck and you will love this tank!
I wanted a 350 but couldnt talk the wife into it...What can you do?