Fish in QT dying

[fishoholic]

Some fish can not handle copper treatment, I have seen it kill small fish within minutes of treatment. While it's good to QT unless the fish shows signs of being sick and needing treatment, I would just moniter them in the QT tank for a couple of weeks and then transfer them over or if signs of illness occur then treat as necessary. Also remember water quality is very difficult to maintain in a QT tank so 30-50% water changes every few days is needed to help keep ammonia from building up.