2nd Floor

there are so many things to consider. I took architecture in school so i know quite a bit about support.
Firstly for strength determining. What is your floor made of, Conc, wood, steel. Each category has different load bearing strengths. IE in most houses you will find wood for joists. And in smaller sized apartment buildings typically under 5 stories they will maximize steel, For a large building, Most floors are made of concrete slabs, with rebar strewn inside. the compressive strength of this is massive.

When we design a floor it is always designed to be stressed to the max i.e. live weight and dead weight.

if your unsure how your floor should support. First calculate the aquarium weight, if for example like my tank is 4x2x2 feet so 8square feet. My tank has a total weight of about 1500lbs divide that by square footage to find out how many pounds per foot.

Last thing you may want, typically for wood or steel joists the spacing between the joists, also are there columns or structural walls running nearby to help span the weight.