I would think about putting some more steel under the house as well as more cinder block piers before trying this. Steel beams are far stronger than we usually suspect, but don't overestimate their strength. The longer the beam, the greater the deflection you'll experience. The beams will probably hold the tank, but your floor will be all wavy! Look up the construction code for the "Live Load" and "Dead Load" for which your floor was designed. "Live Load" is stuff such as furniture, people, and objects that move in and out, while "Dead Loads" are permanent items, and include the weight of the floor/roof. Codes are written not only so floors and roofs are built to safely hold themselves up, but also so they do not experience great deflection under load. However, if you get close to or exceed the loading specified in the code, you're at risk of doing some damage.
If you had the floor plans and beam sizes for your house, as well as the tank dimensions, I could take a stab at calculating the loads you'll see. This is the kind of stuff I do here at school!