That pale crust on your roof isn't algae — it's lichen, and it's anchored into the shingles

Florida roofs commonly develop dark streaks from Gloeocapsa magma algae, but lichen is a separate organism — a symbiosis of fungi and algae — that appears as a pale, crusty gray-green patch rather than dark staining. Unlike algae, which grows across the surface, lichen produces root-like structures called rhizines that physically anchor into the granule layer of asphalt shingles, punching microscopic channels into the material underneath. Those channels allow moisture to reach the shingle substrate, which accelerates wear in a way that surface algae alone doesn't cause.

The treatment challenge is just as distinct. Soft washing with the correct chemical solution kills the lichen, but the dead organism doesn't simply rinse off right away — the remains detach gradually over subsequent rainfalls, so a treated roof may look unchanged for weeks after a successful job. Trying to scrub or blast it off faster pulls the rhizines out along with the granules they're gripping, damaging the very surface you were trying to protect.