Here's an interesting read on floor loading:
http://badmanstropicalfish.com/articles/article28.html
Ultimately, you need someone (eg. an engineer) to look at your specific set of circumstances to answer your question. Just because I was told I'm good to go for my 210 gallon in my dining room upstairs with no needed floor modification doesn't mean everyone can.
There are ton's of factors to consider, only some of which include:
What is the span of the floor joists in that room?
What are those joists made of? TJI's, Fir, Spruce, Hemlock... these all have different loading parameters
What is the floor joist spacing? 16", 19.2", 24"
What load are those joists already carrying?
There may even be a possibility to find out what size footing there is under your foundation. Tons of info needed to make a proper and educated decision on a tank that size.