As long as it is against a load bearing wall, the 125 would be just fine.And a load bearing wall would be one in the middle of the house, or the outside walls. Basically, put it agains the wall connected to the hallway. Most floors are made with 2x6, walls are 2x4-2x6. A well built house has 2x12 on all floors. On top of that all floors have 1/2-3/4 plywood on top of that. Most floors can hold a car or truck. I would not be worried about a couple years of a tank sitting there. Now if the tank were to suddenly jump up and down, I would worry.
Have you ever seen that episode on Geraldo of the 1200 lbs man?
Think about that, he laid in bed for years, middle of the floor, and other people would be in the room, sometimes up to 1600+ lbs, and they had to tear out walls to get him out. That house had a full basement, never crashed through. And he was not against a load bearing wall