Going to post it here just so the thought isn't lost krocky...
You need to put a piece of plywood on top of that stand. As is, the tank is NOT distributing weight over the legs of the stand, but is rather resting on your 1x4's lining the frame. This is putting tremendous shear stress on the screws attaching them to the frame. If any of these were to fail, your tank would be in trouble. By putting a piece of plywood down over the whole top of the stand, the weight from the tank will be evenly and safely distributed over the entire surface area of the wood.