The biggest issues you run into with this is which way the floor joists are running and remember to keep it by a wall. Its better if you can span multipule joists then to grab just one or two, if there is a way to figure out how the joists are run under the floor it would help with the location of your tank safely. BUT a tank of that size should be fine as long as the tank is next to a supporting wall or an outside wall. and the joists run perpindicular to the tank so that you can snag 3 or 4 or how ever many joists you can.
Just doing a quick calculation on your tank size its no bigger then a 75, you should be well with the limits. But still keep to the rules.
I have installed a 280 salt water on the third floor of a guys house before, he had the new engineered joists and had everything checked out prior to putting it up but all looks good regardless. It could be possible to put the larger tank upstairs, just make sure you check your house out very well before hand, you can even brace the flooring from below if its out of the first floor and you have a basement.