What's that ugly stuff growing on my roof!

All of that ugly staining is actually organic growth on your roof. In Florida we have 3 main culprits; they are algae, lichen, and moss. Virtually all roof stains are organic matter in various stages of growth and decay. The black roof streaks you see are actually An algae known as Gloeocapsa Magma, which is the most likely culprit this algae affects nearly 80 percent of the homes across the United States. Gloeocapsa Magma is a species of algae that causes black streaking and discoloration on asphalt/fiberglass shingles. The black staining you see on many roofs is caused by the life cycle of algae and fungus spores that land on houses via wind or wildlife. While this algae can grow just about anywhere, it prefers humid environments such as Florida. A preferred food source of this algae is limestone which is used as "filler material" by most shingle manufactures. Higher quality shingles are manufactured with preventative measures such as copper or zinc containing granules. Several methods exist to prevent and clean infected areas. Installing zinc or copper strips near the roof ridge can prevent further algae growth. Application of bleach (non-chlorine) can aid in removing the stains, as well as many available commercial cleaning products. Some products may harm vegetation beneath roof eaves or near downspout extensions. While many remedies can be performed by the home owner, we recommend the use of qualified professionals due to the extreme danger and risk of injury or death associated to roof repairs and cleaning.
An algae, called Lichen is a fungus and appears as white dots that look like barnacles and range in size. The moss appears as a green fuzzy mass.
Many homeowners have spent thousands of dollars replacing shingle roofs that could have been restored to a like new appearance with simple low pressure cleaning. Those black streaks on your roof are not signs of wear, but algae that can be pressure washed away.
Remember that not every roof cleaning or pressure washing job is the same and the results can vary depending on the condition of the existing roof shingles that are going to be cleaned. No pressure cleaning and low pressure cleaning are very effective techniques for cleaning roofs and can be done without causing damage to shingles.
High pressure Pressure washing is never recommended because it will remove a large amount of the ceramic coated granules from your shingles, which will void the warranty. If you have ever cleaned out the inside of your gutters you will notice granules in them just from the rain taking them off. Think what High pressure cleaning would do to your roof. For instance, you see someone cleaning a roof with High pressure and it appears they have done a good job just because the streaks and discoloration are gone, but guess what? So is a large amount of the protective ceramic coated granules which insure your shingle's warranty. Nobody wants to replace a prematurely failed roof due to an incompetent roof cleaning contractor, and you shouldn't have to.
Soft washing is more time consuming but it is proven to be better for the customer. Soft washing is a gentle and non abrasive yet highly effective means of cleaning your roof while leaving it damage free.