I have yet to find anything that eats when it is that long either... I gave in and removed the worst of the rocks and scrubbed followed by Hydrogen peroxide treatment.Yikes. I haven't found anything that will eat it when it's long. My last tank I battled and finally did a 7 day black out and it knocked it down, but also had some coral deterioration.
I'm surprised he didn't suggest urchins, but I think you already have some (3?)
I have one patch of UFA (Unidentified messing Algae) that's about golf-ball sized and I just leave it out of frustration. My foxface and tang just look at me like "What? We're saving it for later."