I had a problem with a 125 SW predator tank in a 150 year old house in NH. After 3-6 months, the wrought iron stand was pressing down and bending the floor boards.
We dug a small pit in the dirt crawl space under the aging floor, filled the pit with quick-dry cement, put in a small lifting crank, lifted up the joist, put a 2 x 2 perpendicular across the joist to distribute the pressure and put a 4 x 4 post between the concrete pad and the 2 x2 cross joists. Then we put some 2 x 2s under the feet of the tank stand to distribute the weight across the floorboards.
Overkill, perhaps, the 2 x2 s under the tank stand were probably enough, since a refrigerator puts more weight on a smaller area, but better to be safe.