FYI... I was a senior executive for one of the largest roofing manufacturers - for 13 years. Here are some thoughts:
a) Dark Streaks.. it is algae.
b) Warranties... most manufacturers give 10 years
c) Protection... is from a small amount of copper (some may use zinc) as a coating on the granules
d) DO NOT... accept a simple roof cleaning; insist that it is multiple years; most cleaning only lasts 2; another option is zinc or copper strips they can add at the ridge of the roof system
e) Avoid - IKO, ATLAS AND TAMKO... they don't have the best reputations for honoring warranties
Hope this helps.
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