bubble algae spreads like herpes, i'd pull the rock, scrub it real well, and hope really hard. my girlfriend bought a rock covered in it because "it's so pretty" but it took over swiftly. that was almost a year ago and there are still outbreaks even with 2 emerald crabs in a 29 gallon. i also have some bubble algae muscling in on my acans and they aren't happy about it, but i can't really justify an emerald in my 2.5 gallon.i guess manual removal will have to suffice