Green bubble algae is one of several species of Valonia algae. It can become a nuisance in reef aquariums, over-taking desirable Coraline algaes and choking out polyps and corals. The solution is to get one or two Emerald Crabs, Mithrax sculptus, which are primarily herbivores. These crabs seem to love to eat Valonia algae and have helped us clean up Valonia in several of our client's aquariums. Be careful though, as once the Valonia is gone, the crabs may start eating polyps and may need to be removed. We have used these crabs for Valonia control several dozen times, and have only had to remove them in half a dozen cases. There are several species of Emerald Crabs and the tendency to eat polyps may be species-specific.
I done some research for you I hope this helps.