Bubble algae is one of the most common algae in saltwater tanks. It is also one of the most difficult to eradicate once it is established. The best way to deal with bubble algae is to not get it in the first place. You should avoid purchasing rock that has bubble algae on it, and remove the algae it as soon as it appears.
About Bubble Algae
Bubble algae is the common name for several species of macro algae that grow on rocks in reef aquariums. They appear as green pearls that grow singly or in clusters. They grow fast and can crowd out more desirable corals and polyps.
The easiest way to remove bubble algae is to pick it off the rocks with your fingers. Grasp the bubble near the base and just pull it off. Try not to break the bubble. For small pieces of rock, it may be easier to take the rock out of the aquarium before removing the algae.
Some aquarium inhabitants will eat bubble algae. Emerald crabs will feed on it, but there are several species sold as emerald crab, and they are difficult to tell apart. Rabbitfish and some tangs will eat bubble algae, but it depends on the individual fish. Diadema urchins will eat it, but they will also consume desirable coraline algae and may move your rockwork around.
Bubble algae grows under a wide variety of conditions. Even with perfect water and low nutrients, it still grows. You can't starve it out once it is established. With a heavily infested tank, your only option may be to empty the tank and clean and dry the rocks.