The answer
Black streaks are caused by Gloeocapsa magma (blue-green algae feeding on limestone filler); moss rhizoids lift shingle edges. Never power wash (strips ceramic granules and voids warranty). ARMA Protocol: Apply a 50/50 mix of household laundry bleach and water using a low-pressure sprayer, let dwell 15-20 min, rinse gently with a garden hose. Wet surrounding plants with water before and after to protect foliage.
Sources
This answer is drawn from the standards and guidance below. It is general information about how these systems work — not a diagnosis of your property.