Copy pasted from your other duplicate question, one will likely be deleted by admin. I figure I mise well answer both.

Well think of it this way... 100 gallons of water weighs roughly 834 lbs, figuring in the weight of the tank and fish/rocks/etc. your probably looking at roughly 900 lbs of weight.

So then the question is will your apartment floor hold 900lbs on a single location?

Extremely helpful link: http://badmanstropicalfish.com/articles/article28.html

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Aquariums up to 55 gallons can be placed almost anywhere without much worry at all. Many tanks larger than 55 gallons and no more than 125 gallons will be okay, if they are placed in a good structural location and your floor framing is free from significant defects. For example, a 125 gallon tank, on a wooden stand, placed perpendicular to the joists up against a bearing wall, will often be okay without any additional structural support. If your tank is over 125 gallons, then it is likely that you should consider adding supports under your wood framed floor. Please realize that these are generalities that may or may not apply to your particular situation.
End Quote---------------------

So it's likely unless you have some shotty construction a 100 gallon fish tank is okay if properly placed in the apartment.

I would also ask your landlord if this was okay. Many buildings have rules against both water beds and large aquariums due to the risk of water damage should they break.

Hope this helped.
Source(s):
http://www.epa.gov/ogwdw000/kids/water_trivia_facts.html

check with your landlord (or property management) about the construction. Find out how old it is, and if the walls/floors are reinforced with anything. If there's support beams across the ceilings, thats a good sign. If it's a cheaply built plywood/particle board and drywall place, then no. if it's brick and mortar construction, you're okay. Keep in mind, some walls are load bearing and some aren't.

I had a 300 gallon tank that we placed over a brace on the second floor of the house - the tank was essentially over where another load bearing wall came out downstairs. We chose the location carefully. This was in an old house that was slowly being eaten by termites. The floor creaked while we were filling it up, but after that there were no problems. A 100 gallon should be okay.

The tank would be safest in a corner or up against a wall as opposed to the middle of the room.