You could stop adding, or you could do a water change without any additions besides ALK buffer, b/c it is most likely really low.
Im pretty sure a copper band butterfly is reef safe. People use them in their reefs to get rid of Aptasia anenomies. But they might pick on some corals, like mushroom anenomies. Other people will have to comment on that. I would say they are medium hardiness, not all that difficult. Expense- in Buffalo they are like $40 or so.
Steve