i have a 125 gal on my top floor above my basment. crazy indeed for even concidering it. first off, a coal mine collapsed a few years ago under our house so everything was cracked etc. also our house is well over 60 years ago, but with high quality wood, where you cant even drive a nail into it without killing yourself! so, the coal company came and ran 2x6 beams across the now unsupported areas, then jacked the beams up with jacks. where my tank is, 2 2x6's screwed together, are about half length of the tank, so only half of it is supported to the least. what we did is jack up the other half to compensate with a 6 or 8 ton floor jack, and four months later, Aok! simple thinks like the way the floors run and supporting walls etc, as well as your stand size can all benefit when a decision like that arises. a 125 gal is normally 6x18"x24" so i made my stand (4x4's, 3/4" ply) about 4 inches longer, and made it 24 inches deep so the footprint is much more evenly spread. i never did go the route of engineers etc for hire, but just evened the odds out with obvious saftey and bit the bullet!