What eats hairy algae???

[Bemmer]

Can you tell me which invert is best for eating hairy algae off the side walls and my LR?

 

[The steven liu]

Long spine urchin is pretty good at doing that, except it'll also take care of coraline algae and sometimes sps. You can try a lawnmower blenny if you can find one. I had an angel fish which used to feed on hair algae off my tank wall, unfortunately it also fed on xenia polyps.