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Looks like hair algae to me. He needs to lower his phosphates (and nitrates) and get something to ear it or remove it by hand. Also, you can try flux rx which works on some hair algae (and bryopsis). It doesn't appear to be feathery like bryopsis.
I was going to suggest fluconazole as well given the advanced stage, but OK.
Get some pics under white light and compare to this for ID & suggested actions:
A Simple Guide To Common Problematic Algae And The Means To Control It..
As we all know algae is inevitable in both Marine and fresh water aquariums and if not watched and without proper procedures for removal can quickly turn a beautiful aquarium in to something that resembles a scene out of a old Swamp thing episode. Some are easy to control some are a non stop...www.reef2reef.com
Aside from a sea hare, nothing is going to eat mature stuff like that. Most herbivores prefer the tender new shoots.
Lastly, I know @brandon429 has some treatment threads to suggest to your friend. Some elbow grease is required.
I told him he needed to reboot and put in nuly cycled rocks. I think it's the old tank syndrome because all rocks came from his 150 that had been running for some years and he had issues with that tank.
No, it didn't work at all. He's gonna Vibrant and see if that'll work. I hope it does because I don't want to reboot his tank. Has a few sps but mostly LPS and Softies. It's a 220 gallon tank.