that sounds awful dangerous to me
is your foundation concrete, or your subfloor?
if your subfloor is concrete, then you are OK with about 5 to 8000 lbs anywhere you want it, depending on slab thickness, rebar / remesh, and the type of cement used.
if your foundation is concrete with wood 2x6 or 2x8 joists supporting a plywood subfloor overtop a crawlspace or something, then you deffinately will want to double check positioning of the tank, and go with renforcements like logan has suggested. A general contractor or structural engineer would be able to sell you how much reinforcement you need... logan's sounds "excessive" but always good to err on the side of caution!