I am pretty sure my floor joists are engineered floor joists because it looks like this
http://www.icreatables.com/framing/w...or-joists.html
I double check in the basement, there is at least 1 joist below the tank. the tank is positioned from half the distance from load-bearing wall - 1st joist to half the distance from 1st joist to 2nd joist.
So the first joist takes all the hit.