All you pressure washing experts... How do I get old mildew/mold stains from brick house.?

I bought industrial strength Concrete and driveway cleaner that says is useful for brick as well and this did not help. I pretreated the house with my pressure washer at a low pressure and then used high pressure to wash it. The dirt and even some of the grout/morter came out but the black mold stains still are there. I even tried it full strength and this still did not help. Does anyone know of an acid or something a little safer than acid to use to remove this from my brick. I am sure it has not been cleaned in a longtime. I have all the dirt removed I just need the stains removed.