I agree with Rene.. I mop my roof spring and fall with Spic & Span and do not usually see much mold (Did see some green in GA but hey. In Ga there is lots of Green.. Mopped an extra mop and away it went)
I use a long handled "Van Wash" brush. instead of a mop. A bucket, Spic & Span, and a garden hose with sprayer..
Does a good job.. Roof is still white.. Roof is 13 years old come spring.