going solely off of memory back from the reefcentral and reeftank days I believe there is a red variety thats worth looking out for but most others at worse just get a big population boom and can be unsightly until things balance out or predation beats them back. Flatworm Exit used to be used but some varieties can release toxins when they die. In short I'd bet they've been in there for a long time and if you have a wrasse your likely fine.