[pogodzib]

A lot of people have set up 125 gal tanks on their main floor. Even worse is setting up a 120 gal tank on the main floor since the weight is only spread out over 4'. Depending on how well your house was built and how old it is, you may be able to set it up without adding any additional support under your floor, but most often, adding some additional support in your basement is a good idea. If you can get an architect or civil/structural engineer over, they should be able to tell you what you can and cannot do.