what is this & how do i rid myself of it

[3m]

when i bought my new to me tank the rock the guy had in the tank was covered in this. what is it and how can i rid myself of it & makes sure it wont come back.

 

[cranberry]

That is so hard toget rid of, it's red turf algae. Nothing much seems to eat it.
I hear long spin urchins do though......

 

[3m]

do Dolabella Sea Hare's eat that?

 

[cranberry]

I don't know. Sorry.