Algae can be removed from aquarium rocks by manual scraping with a toothbrush or algae scraper, boiling the rocks, soaking them in a diluted bleach or vinegar solution, dipping them in hydrogen peroxide, or introducing algae-eating species such as snails and shrimp. Commercial chemical treatments are also available. Regular water changes, proper lighting, filtration, and avoiding overfeeding help prevent regrowth. Always rinse rocks thoroughly before returning them to the aquarium.