Not had CRS long enough to tell you, but RCS eat hair algae, thread algae, they pick at GDA not really eating it, and possibly diatoms, but I never had them so I can't tell you. They do not eat BGA, GSA, BBA, and clado.
I don't think you should really rely on CRS for algae control. CRS are more scavengers than algae eaters from what I have read.
Edit: O you meant RCS. ok lol. forget my comment on CRS