lol a 980 is not going to be any good for livingstonii for very long either, they really need to be a in a big 5fter or a 6fter as they are big predatory open water fish..
If it is the smaller ones then I would suggest the tank is too small and they are just getting chased too much and it is causing them to get a bit ragged, getting them into a bigger tank would be my suggestion.