The dark streaks you see on your tile roof in Tampa are an algae called gloeocapsa magma. This fungus is transported by airborne spores, and by birds, squirrels, etc. Once attached to the tile roof it begins to feed on the organic matter found in your roof. If left untreated, it will continue to grow and spread, until the tile roof eventually becomes totally black.
This Algae can cause tile roofs to fail prematurely, and it can raise your utility bill. You should never pressure wash a tile roof, it will shorten the life span of your roof, and cause more damage as well .
Apple Tile Roof Cleaning Of Tampa uses a no pressure spray application to kill and remove the algae safely without damaging your tile roof.