This stuff is all pretty basic Internet usage. Isn't it time to learn a bit about how to use the medium we spend so much time with? (nothing personal)
Dave.M
Looking good!
Will the tank be running perpendicular or parallel to the joists? As far as material, and what to use, 4x's from floor to cieiling should be ok, but you may be able to get away with cross bracing each of the joists....either way, I would consult a structural engineer just to be safe