If it doesn't appear to be growing then remove it. You can do this by using a syphon hose (lots of people use airline tubing) and then scrub it with a toothbrush. Make sure it's a new toothbrush cause you don't want to add toothpaste, I don't think the fish need it lol. As you scrub the algae syphon it out. You need to ensure your nitrates and phosphates are in check or it will grow back. You could also add something to eat it but I would recommend you try to avoid this approach. If you do go this route then I would avoid fish, a sea hare would be the best option. Problem with that is that once the algae is gone it will starve to death so it has to be removed and passed on to someone else with algae issues. My LFS actually has an exchange program in place for sea hares.
