I would have claimed the basement for 'Fishlandia'. LOL
I have seen some pretty extensive damage from water, and weight is a whole other thing to consider. Every now and then I will have a little nightmare/daydream about a busted tank, or a tank that tips over, or the floorboards caving in.
shudder 
In my house, where I do have a few tanks, I am on a crawl space, and have added jacks to provide some extra support, and peace of mind.