I had the same prob in my apt on the 3rd floor. I did some research, and same as Brian said put it on an outside wall, not a *false* wall. If it can support the building it will be able to support anything you can fit on your second floor (most likely unless termites, ect...). Also I got renters insurence for $10 a month, they have never heard of a fish tank falling through the floor, but said they would cover it. It was coverage of somthing outragious that they would cover. So if they are willing to risk that much money they must be pretty confident that it won't fall through. Call and ask your home owners insur or renter insur and ask questions....I had a 90gal on an outside wall 3rd floor. No probs