Getting rid of stains on shingles depends on the type of stain, whether it is black algae streaks, moss, rust, or general dirt. For the most common black algae stains caused by Gloeocapsa magma, use a shingle-safe cleaning method recommended by manufacturers. Mix oxygen bleach, sodium percarbonate, with water and a small amount of mild dish soap, about one gallon water to one quart oxygen bleach. Apply with a low-pressure garden sprayer from ridge downward on a cool, overcast day to prevent rapid evaporation. Allow to dwell 15 to 20 minutes, then rinse gently with a garden hose on low pressure, never a pressure washer, which strips granules and voids warranties. For stubborn stains, commercial products like Spray and Forget, Wet and Forget Outdoor, or Roof Shampoo are effective and require no rinsing, working gradually with rain over weeks to months. For rust stains from flashing, you may need a specialized rust remover safe for asphalt, but test in an inconspicuous area first. For moss-related green stains, kill moss first with zinc sulfate or potassium salts, then gently sweep dead moss after it dries. Always protect landscaping by soaking plants with water before and after cleaning, and avoid chlorine bleach which can damage shingles, corrode metal, and kill plants. After cleaning, install zinc or copper strips near the ridge to prevent future algae growth.
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