will a 150 gallon need a re-enforced floor?

[Pazil]

How old is the house? What type of floor joists?

If they are "I" beams and the span is not more than 12' you should not have any problems. If you are in a newer home you could contact the builder for set of blue prints and figure out your live and dead load capsities from there... But I would at the very least build the stand with a 3/4" plywood base to spread out the load and ensure that it is sitting as per your drawings. With the tank that close to the beam below on your drawing I do not suspect you will have any issues.