I am an engineer- however I am a mechanical engineer and not a civil so this is out of my realm of expertise.
However I would suggest that you do several things
1) Talk to the landlord first
2) Think about what you will do if you have to move one day
3) If you decide to still get the tank look for a way to distribute the weight across a large space.
FOr example some tank stands put all the weight on the posts so it is distributied on four spots. SOme distribute it across the length and width of the tank. I am sure you coudl look at putting some type of structure beneath the tank stand to spread the weight out over an even large portion of the florr. The more you can spread it out the better.