Stackiing Tanks to free up floor space

I decided to reduce the floor space my tanks were taking up so I built a double-double stand for the small tanks. The stand holds two 29's on the bottom and two 20's on the top. As built the stand could hold two 55's instead. So now the fish room looks like this:

Double stand 1 - 55G on top, 40G long on bottom.
Double stand 2 - 55G on top, 40G long on bottom.
Double stand 3 - 2x20G high on top, 2x29G on bottom.
Stand 4 - 55G
Stand 5 - 55G
Stand 6 - 38G
Stand 7 - 2x10G

I've taken two 55G and a 29G/20G stand (29 on top, 20 on bottom) out of service. My brother just asked me to take his 75G since he's tired of it so it's a good thing I freed up some room.

The stands are designed for two 55G and have had that combo on them before. The reason the 40Gs are on the bottom is ease of getting into the tank, being two inches lower than a 55G.

As to the new stand, yes I'm testing it with a single 29 right now but I don't expect problems. It is built out of 2x4s and held together with 2.5" stainess steel deck screws (had a box leftover from the deck rebuild). I plan to paint it and am debating about decking the shelves with some excess plywood I have sitting around. One of the other stands is decked and the other is open framed.