Short answer: you should be ok.
Longer answer:
Depends a lot on your stand, both in how heavy it is, and how it distributes the tank weight. One key point in this is how much surface area of the stand touches the floor; i.e., a smooth bottom will distribute weight more evenly than, say, those iron stands with four small feet.
For info, water weighs 8.4 pounds/ (US) gallon, so 50 US gallons of water weighs 420 pounds. Also, if you have gravel in it, about 2.5" thick, it's probably 100 pounds or so. All in all, I'd guess your tank weighs around ... 700-800 pounds, depending on your stand and how many rocks you have inside.
One good thing to do in regards to weight is (if possible) to put the tank parallel to (and up against) a load-bearing wall, so it spans as many floor joists as possible. Outside walls of a structure obviously are load bearing, but it may be tough to determine which interior walls bear load in an apartment complex (generally, the space between parallel load-bearing walls is 12-16 feet, ... I think).