Roof Stains

Hi: Although a lot has been written about algae-moss-moss, etc. on roofs, it's still difficult to diagnose. The stains are black in dry weather and red after a rain. There was also moss growing but I think I killed them off last fall with a number of Safer applications - also Bayer - for roofs. The tufts of moss at the edges of the shingles turned orange from their green, growing state and look to be kaput. However, the stain persists. My guess is mildew, but I'm not sure and don't know how to be sure about what it is. Also, because it's a 12/12 roof, I'm not about to go up there and scrub it. Any suggestions on how to diagnose and treat it would be, of course, appreciated. There are many roof cleaners on the web but they also deal in a lot of hype and fear-mongering, so I don't trust them at face value. If anyone has used any of them successfuly, please let me know...
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