There are lots of technical questions/ answers involved but I try to keep it simple. Water at 8+/- pounds per gallon gets you around 320 pounds, add some for rocks and tank and you come in under 500pounds, easy. So would two large guys weighing 250 each be likely to damage the building? I don't hear of it happening and feel the codes would need changed with lots of the folks I see. I call it safe as that is not really one of the bigger tank sizes.
These things tend to be slow moving, long term problems if they do happen. If the building is in somewhat reasonable condition, I don't give it any more thought. If the building won't rent to football linemen, reconsider!