Many customers read that zinc strips and copper strips should be installed because they will keep algae (gloecapsa magma) or (Black stains) away. Well this is mainly false because these types of strips rely on rain fall in order to work. These strips only keep algae, mold, moss, and lichen away from the top areas of the roof were the strips are installed . I cleaned a roof that was 6 yrs old in Andover Mass and the home owner had zinc strips installed and the algae, mold, moss, and lichen was able to grow on that roof. here are the pictures to prove it. Zinc strips and Copper strips are installed at the very top of the roof and if you look close enough , these type of strips are installed on this roof. Also notice were the roof has remained clean and these strips were installed when this roof was brand new. Copper strips and Zinc strips will not keep the roof clean, the only way to get the roof cleaned and keep it clean for up to 5 yrs, is to have it professional cleaned by a certified , non-pressure soft washing method.