I am adding a large fish tank (65 gallons) to my second floor and would like to make sure to distribute the load across as many joists as possible. Is my best way of doing that to build a long, short platform to set it on?
Here is the general idea, where dashed lines are the joists, solid black lines are the box (basically a structure of 2x4s screwed together with a piece of sheathing on top), and the orange is where the tank would go.
If that sounds like the best way, then the next question is as to whether the positioning of the wood matters - i.e. using a 2x4, I can lay the base down by the 4 (making it easier to stabilize).
Update: This is close to the main bearing wall, however the old tenants moved the original wall in the basement (over by about 6-12 inches). This caused the house to shift a little and you can see that via a slant in the flooring. This is why I'm resistant to throwing that much weight in an idle configuration.