I would just use a scraper if it was on the glass, but it isn't. The algae only grows on the live rock.
I change about 20% of the water once a week, so the nitrates aren't out of control. They are a little high, so are the phosphates, so I'm pretty sure they are the cause of it. I don't have the money to invest in an RO unit, so what other options do I have to get rid of this stuff?