We have a pretty good crop of Bubble Algae (Valonia ventricosa) now with no idea how it got started. And we let it get out of hand. The tank was free of this nuisance from the beginning and started about 9 months after setup. Nothing was added except fish prior to the break out.
Note that for us, the presence of this algae doesn’t bother us.
But, we added a few Emerald Crabs as a test. They are chipping away, but it would take many, maybe 10 or 20 to dent the problem. Ours are eating very small bubbles and ignoring the large ones.
Remove them by hand? Not easily and would likely knock over the rock work if we picked and shoved manually. Some of our rocks are just stacked on each other, not cemented together. Maybe a mistake looking back, but we wanted the flexibility to re-arrange.
So, out of nowhere, one of our fish rides in to the rescue. Out of the blue, a fairly large Yellow Tang starts ripping away at … the bubble algae. This one fish is keeping any new bubbles in check and little by little reducing the problem.