Everything I have read about them says they only eat apista. But if you only have a 1 or 2 Berghia are overkill, they should only be used when you have plauge level of apista as they will soon die after all the apista are gone. If you get berghia just keep an eye on where they go, if you see them chilling on your BT then you should kick them off, and move your nem to a place they cant get, such as sump or even worst case into a bag at the top of the tank with small holes for waterflow haha.