I bought like 10 of them. I thought they had died, then the other day I see a good sized one deep in the rocks. If it had not moved I wouldn't have noticed him at all.
They need lots of algae to survive. As long as hair algae is lingering in my background I guess he has plenty to keep him healthy and happy. He serves his purpose, I don't have any hair algae that can be seen with the eye.