Generally they are bad guys and it depends what corals you have that it might feed on. Worse actors are zoa specific and , monti specific. But there are also aiptasia specific ones that folks buy and sell to deal with those . If you see one there are probably more.
Small chalice frags can be tricky. I've had that same problem if the frag isnt "aged" enough before you move it in. Try to buy frags that have been growing for awhile instead of fresh cut .