[lynnvangsnes]

If you are able to remove the rock and manually scrub it, then do so. If this would disrupt your entire aquascape, then consider during a water change, put a siphoning close to it and use a toothbrush or something similar. The stiffer the brush, the better. This may require two people. I don't know how long you have. I have seem them get as big as marbles. I do get them from time to time, as they are very difficult to get rid of completely. Just keep after it and one can keep them in check. I would avoid getting an emerald crab just to eat one bubble algae; after all, what will it eat when the bubble algae is gone?