The black streaks on your roof are an algae known as (Gloeocapsa Magma), this is an airborne algae that can spread from roof to roof. If not taken care of soon it may take over an entire neighborhood.
PRESSURE WASHING -There are many pressure cleaning companies out there that claim to offer roof cleaning, but really all there doing is using a high amount of pressure to remove the black streaks which doesn’t take care of the problem, it only makes it worse. Using high amounts of pressure on your roof will void any warranty you may have on the roof and also take well over half the roof life off your roof by removing the granules of the shingles or by opening up the pores in your tile roof allowing the algae to grow back twice as fast, which will lead to permanent roof failure and the need for a new roof.
SOFT WASHING – This is the only approved method for safely cleaning a roof according to (ARMA) Asphalt Roofing Manufacturers Association. This process is done by using no more pressure than a garden hose and 100 % biodegradable chemicals to apply the roof cleaning solution to the roof to chemically treat and remove all algae, moss, lichen, and mold, leaving the roof looking brand new again. When used correctly by a trained technician it is completely safe for pets and plants.