I'm getting a 120g in two weeks and was curious about the weight it would add to my dining room floor. After much research, I found that it will weigh between 1200lbs and 1400lbs with rock and water, and I'm going to need to add some support under it. I want to say that I'm not a professional and while I did consult professionals this is by no means to be a substitute for you doing your own research or hiring someone to do it for you. This is just my DIY story. My dining room is floor is supported by 13ft 2x8 joists spaced 14.5 inches apart. The aquarium is going to run parallel with the joists and sits above a basement with load-bearing walls on each side. The weight of the aquarium is going to be spread over two joists almost exactly center. From my research, I found it wasn't that the aquarium will come crashing through the floor but would cause the joists to sag and that side of the house to become unstable. I decided the best route for me was to add a floor post. This is where I started asking a couple of contractor friends and engineers for their thoughts. The best route was to get a metal plate or bar under the joists supporting the tank. Unfortunately metal is crazy expensive right now. It was going to cost me over $500 for just the metal. My brother who works with aluminum had some extra strength aluminum bars laying around. We did some checking and found that this would be adequate for my needs. I was still a little hesitant using "extra strength" aluminum so I decided to add another support post. I also did some blocking inside and outside the area of the aquarium. That will provide some extra support and reduce any bounce in the floor. In the end, I used two floor posts both capable of supporting 12,400lbs each, and two extra-strength aluminum bars to support the two joists the aquarium will sit on. In all it cost me $180. Here are some photos of it all finished. oh, the floor was a little uneven so we had to setup the bars differently.