Roof washing requires skill and knowledge. Skill and know-how are required when washing roofs.
The best way to clean older roofs is with a soft wash system.
It is not just unsightly, but algae and moss can cause significant damage to the shingles as well.
The debris on your roof does not necessarily have to be visible from ground level to cause damage.
Soft power washing your roof is not an expensive service, but it is a valuable investment in maintaining the appearance of your house.