Several of the darkened thin objects found on roofs are actually fungi and not bacteria. There is a differentiation between bacteria and fungi and how your roof is damaged. Bacteria also depend on the Portland cement in shingle roofs, while fungi often thrive on plants and other organic compounds that are accumulated on your roof. People have done little to avoid spreading bacteria and dust mites through the air and falling on your roof, and you can help prevent growth of microorganisms by maintaining the shingles free of plant material.
Owners in Cedar Rapids and surrounding counties usually let the mixture of bleach and water sit in the affected area for approximately 5 minutes, then rinse the mixture with a hose. However, for many reasons, bleach is not an appropriate solution: it kills and damages pant properties and it can hurt the current status of your roof tiles if it is left on for too long or not completely rinsed off.