I stumbled upon a way to get rid of bubble algae.
At first, I would p#*!k it with a long, skinny, sharpened, solid siphon tube attached to a syringe, sucking up the gooey inside so as not to spread it. This worked okay, but it still let some of the gooey insides out.
I left it alone, until one bubble got to be about 3-4mm, and I was curious, so I touched it. I discovered it had a hard shell.... Hmm....
So I wiggled it, and it popped right off the rock! I tossed it out.
Another piece had grown, this one about 6mm (pretty big), so I tried to pop it out too. It was more difficult, and required very gently, patiently wiggling it back and forth until it popped out too. So far I've been lucky in that each piece that's grown was reachable by hand. I've hand-removed all of my bubble algae, and have not seen any in over two months!
BTW, pick them off when they are less than 5mm or so, the shells on the smaller diameter are harder, and you can wiggle them with more force than the larger ones.