So the good news is I was able to move into a studio apartment on the ground floor with up to 2 fish tanks allowed in the lease, no gallon or size limit specified. I don't want to be a jerk and ruin the floor though. How do I figure out what size tank I can safely keep? I'm hoping to put a 75 gallon in. I will try to measure the floor joists for a PSF calculationand figure out the joist orientation with a stud finder as wel, but I don't know how to factor in the age of the building. It's a 1920s Victorian style house subdivided into apartments. Can anyone give me some tips? I've never lived in an older building before and don't know what to watch out for. Thanks in advance!