apartment buildings are constructed very differently than homes and can bear heavier load. in addition to holding more water, king water beds have a larger footprint than a queen water bed and both have exactly the same weight per sq.
look, all i am saying is the answer to "can a XXXg tank go upstairs" isnt "sure its fine". joist size, subfloor, placement relative to external wall or beam, etc, etc all should be considered. in my situation, i didnt provide additional support for a 55g tank, but i did for a 75g.