Determining max tank size for my apartment?

[Vagabond]

HELP!!

Any engineers, architects, or construction gurus out there who can tell me how to determine a safe weight allowance for the floor in my 3rd floor apartment.

I live in a wood frame building on the 3rd floor (probably late 70's early 80's construction) and am concerned with the size of tank I can safely put in. What construction information do I need to know and is there a formula to determine how much weight my floor joists will support?

Also what is the best way to distribute the weight evenly accross the base of the tank stand?