Coolant Leak From Radaitor

What could be leaking that is colorless, odorless, and tasteless? Doesn't appear to be heavy enough, and no rainbow shine, like oil. Checked the fluids, not sure how full the brake or transmission fluid should be. Also, do those stop leak products that you put in the radiator?

Just found a spot on the driveway. Had the oil changed, coolant flushed, and all fluids topped off at about 110,000 miles.

Please help me