The only thing you have to keep in mind when using mithrax or emerald crabs, is that when they eat the bubbles, they pop them in the process. Doing exactly what you don't want to do!!!!
I would replace your
GFO if its over a month old and get some fresh stuff in there. Also, it seems that when you moved your rocks you probably did one of two things: popped a couple of them in the process or you might of had some accumulated organics in your rockwork and released them into the water column free to be eaten by those round little eyesores.
Manual removal, fresh
GFO (do you have a reactor for it?), adding more
macro algaes to use up the excess organics, cutting back your photperiod by a couple of hours, or as Carmie suggested for 2-3 days, and then a massive (10-25%) water change followed by smaller, weekly water changes. Attack it from as many angles as possible and it should start to recede.
