Bubble algae, or valonia I believe it's also called, is just a form of macro-algae. It's nothing to be worried about. It's generally brought about by other standard algae growth factors, like nitrates or phosphorus. If it's dying off quickly in your tank it just means that there aren't enough nutrients to sustain it. It starts off small and I've seen some bubbles get pretty large. To remove them just gently shake them and wiggle them until they can be taken off whole. Popping them only means that you're letting alot of little spores all over your aquarium, which can become more bubbles. Like I said earlier though, nothing to worry about. I've also heard that mythrax crabs will take care of them. Mine prefers hair algae, but I'm sure they'll take bubbles too.