I have a friend who's been keeping fish for a year or more. He has two tank , one with Oscar and one of 55 gallon which was actually a community tank of some tetras and large danios. He recently moved the danios and got two few months old white Severum. One unfortunately has a little torn tail..it's not fun rot, slight torn in the middle of the tail, and he has some black skirts with them . So , those two fishes, one is chasing the another with torn fins, like very slight chasing and nipping on its body or tail and he/ she can't relax properly. Any way this can be stopped? And will the damaged tail fin grow back to normal ?