I have some Angel fish with a killifish. They don’t bother each other but I put a new rainbow fish in and my killifish won’t stop following them around and flaring his fins out and occasionally gills. He hasn’t bitten the rainbow fish but he will stay within a few inches of it sometimes just being relaxed and other times following and flaring fins. Is this aggression that I should worry about? Or will they sort it out? Should I get another rainbow to change the power dynamics? Or will this be an incompatible species?