Trio of Chromis Dying

[RedLion]

So do I just add them one by one then, in other words only 1 fish at a time in QT?

 

[Amphiprion]

Not necessarily one at a time, but just be extra careful. Maybe an additional filter on the tank, plus cycling in advance may help you out for new purchases. Of course, frequent water changes will help out tremendously. For a quarantine of that size, the 3 Chromis together are probably the max I would try at one time. Just be sure to cycle in advance for each subsequent quarantine, so don't impulsively buy a fish--plan it out first and be prepared.