Ok so my wife's parents has a gold fish tank that we've been taking care of for a while. There used to be about 6-7 of them and now 3 remains now with a bunch of tropical fish (yes I know they don't mix but they work). We've tried adding new gold fish twice already, but each time the newbies died or don't look good all the sudden and die. Is it possible that the remaining three goldfish are actually bullying the new fish? They don't have a QT tank, but I also thought of QT in my tank and take it back to them in a few weeks.