We recently inherited a tank of fantail goldfish from our nextdoor neighbour, there where origionally three and we bought two more, a black and white goldfish to add to it. There didn't seem to be any initial problems however recently i have noticed that the white goldfish has been nibbiling on the tails of the bigger fish. Im worried that it is stressing the other fish out. The fish only picks on the bigger fish however and leaves the black one who was bought with it alone. I'm hoping there is some way to fix the problem short of compleltly removing the fish, any advise would be appreciated, thankyou. (the tank isn't overstocked) PH 7.6 Nitrite 0 Ammonia 0.25 which i know is a bit high, could this be causing the fish to nibble??