Fish that eat aptasia and/or bubble algae?

[Delphinus]

Don't know about the Pacific sailfin tangs, but my sailfin (Red Sea) doesn't touch valonia (bubble algae) except by accident. By "accident," I mean, if I pick a bunch and maybe one escapes and floats around in the currents, he might chase it down and gulp it before he realizes what it is... But ordinarily the only way for valonia to get out of the tank is by me picking it out. I have 2 or 3 emerald crabs too, and they don't touch the stuff either. Why I always get the fussy ones I don't know, or perhaps "my" algae is just somewhat more foul tasting compared to other people's algae.