saltwater aquarium algae problem

Question
hi, hope you can help.i have recurring problem with a v/dark almost black algae that only forms on my ocean rock.it forms mat with hairs about 2-3cms in length.i clean it off every week but it returns within 2-3 days.also underneath it small air bubbles are forming.i do a 30% ro water change every 2 weeks,use rowaphos,purigen,and check all my nitrates,nitrites and ammonia levels which are all basically none existant! i have asked my local fish shop for help for but got no real answer. hope you can help.... dave  

Answer

    Sounds like bryopsis,{green hair algae] which prduces mats, then hairlike protrusions, then gas bubbles start to form as the algae is dying. Go to about.com and click on "hobbies and games". On the next page all the way down at the bottom left you will click omn "saltwater aquariums." There are numerous articles, pictures and cures for various types of nuisance algae. I'm sure this site will help you greatly. good luck, gerry.