Algae can grow on any surface where the environment is right. Moisture and shade provide an excellent environment for algae growth, so fiberglass shingles, boat hulls, pool walls or any other fiberglass surface can be susceptible. Removing algae from fiberglass is a simple process because fiberglass is not porous. The algae cannot penetrate the surface of the fiberglass, so they will come off with scrubbing.
Remove the water source from the fiberglass, if the fiberglass is submerged. Pull the boat out of the water, or drain the pool to expose the algae stains to the air and make them accessible to scrubbing.
Fill a bucket with water and mix in powdered oxygen bleach according to the package directions. Dip a stiff-bristled scrub brush into the bleach solution and scrub the algae in a circular motion. If you are working on shingles, a long-handled brush may be easier to use.
Let the bleach solution sit for 20 minutes. If the fiberglass begins to dry in this time, re-wet the area with the bleach solution. After 20 minutes, scrub the algae stains again.
Attach a high pressure spray nozzle to your garden hose and rinse the fiberglass with the water. Rinse from the top of the fiberglass to the bottom.