In my experience a foxface will eat it until it's all gone.

red turf
 

Yeah, I had a large foxface until a couple of months ago. My Sohal bullied it til it died. Maybe I always had the red turf problem but the foxface had been keeping it in check for the last few years, and with him gone, the algae took over again. ( funny, the foxface and sohal had been living together for the last 2 years without problems)
Since putting in the 5 long spine urchins last night, I definitely noticed some difference this morning. At this pace, looks like the tank should be cleared up in a couple of weeks. Will keep all posted.

Don't urchins leave a path of destruction wherever they go knocking over corals and things?

I have a fairly extensive red turf problem as well... whenever I do a water change, it puts a noticeable dent in it, but not enough to get rid of it. I'm going to try some Mexican turbos before I go the urchin route.