I agree with the aforementioned comments about your stand. If the front of the stand is built into the walk that should be fine, but the back is concerning:
First, I would not use treated 4x4s - They notoriously twist, bend, and crack when they dry out. 2x4s nailed edge to edge (like a long L) will work much better. Also treated lumber is treated with all kinds of nasty chemical that you would never want leaching out in a reef tank. Do a quick search on treated lumber in stands and you'll find others who made the same mistake and switched them out.
Second, and more importantly, the back of your stand is not structurally sound. The 2x4 in the back should lie between the top perimeter of the stand and the bottom perimeter of the stand. That way all the weight of the top is distributed through the long axis of the 2x4. As you have it now the weight of the top of the stand is only being supported to the bottom by whatever screws/nails you attached the 2x4s to. Fortunately its a quick and easy fix - all you have to to do cut 2x4 to fit in front of the ones have now, such that they sit between the top and bottom frame. Do the same with the corners.
It is a $20 fix and will significantly increase the strength and longevity of your stand.