Your looking at around 2000LBS. I wouldn't do it without reinforcing the floors. That goes for the 2nd floor to or anything that's not a concrete slab.
Hello; A rough estimate for a large tank might be 10 to 12+ pounds per gallon. This can vary with the type of stand and the stuff you put in the tank. So you may be looking at 2000 to 2400 pounds or perhaps more
Here is the web address of an article that talks about the issue.
My take is that the question can only be answered by someone with knowledge of structure actually having a look to see what you have and what condition it is in. There have been posts (a link follows) describing damage from tanks from time to time, so it does happen.
In case some missed this thread a while back here is a link to it. A look at the pictures should give pause, they did for me.