how much weight is too much?

My opinions: chances are that your floor is capable of supporting that weight. Chance always implies an amount of risk. It would be a small investment to ensure that you dont go through an ugly divorce.

 

Excellent placement and the floor jack idea will give great peace of mind.

 

What timing I just found someone tearing down a tank and selling 2 support jacks for 20$ now that would be foolish to pass up

 

and the stars were aligned . . . .

I'd still get the other two for the nightime sleep you would lose otherwise . . .

 

fwiw, when I was placing my 180 in our dining room (now fish room), I would have liked to place in spanning 4 or 6 joists, but with the room layout, I ended up on two joists. I reinforced them with concrete blocks as I was over a crawlspace. it has been about 9 months and all is well that I can tell.

best bet is to make sure your tank is perpindicular to the joists.