You might get a broad platform of thick plywood and paint it, then put your tank stand on it: engineers please correct me, but that should distribute the weight over a wider area, if that is a concern, but if your floors will bear a well-loaded refrigerator, they should withstand your 70. It also helps to site the tank against a load-bearing wall, where the beams tie in head on, as opposed to room-dividing walls, where beams run parallel to the wall. The main thing is not to let the wood get soaked. Then it certainly will bend.