Foxfaces are heroic algae eaters, you just need to keep them fed afterwards because they will continue to graze and will sometimes get a taste for coral flesh. Emeralds are hit and miss, you've got to get females as males favor carrion and meat as they get older. It's fairly easy to tell, there are many ID images online for other species but it's roughly the same for them all.
I have heard very good things about Pitho and Strawberry crabs eating bubble algae, Nemo's just got a group of strawberries in and Reefcleaners has Pitho crabs.