My longnose hawkfish has just recently died in QT. It has been in quarantine for the past 11 days. The fish store I originally bought him from had him for about 4 weeks. He has been eating amazingly and taking both frozen Mysis/brine and the TDO pellets I have been feeding. Last night he refused to eat along with this morning, so I decided to try feeding frozen when I came back from work. When I came back he was acting pretty normal but did have some heavier breathing and was perched up on the aquarium floor. I went to take care of some other things and when I came back to feed he was dead lying on the floor. Currently I am trying to test as much as I possibly can. So far copper was at 2.46ppm, salinity at 35ppt, the only concern is ammonia. I have an ammonia badge in the tank that I have been relying on and it has always read between safe and alert. I am currently waiting the 15 minutes for my red sea ammonia test kit. Currently the QT is a 20 gallon long and he has been quarantining with 2 other clownfish who have been doing completely fine, with only a few issues of aggression between the clowns but none between the cowns and hawkfish. The QT has one large sponge filter connected to an air pump, it also has a powerhead that is on for about half the day and many pvc hides. I am still waiting for the ammonia test as I said but am wondering if I should do anything for the clowns right now if there is a possibility of disease in the tank. Thank you, attached below are photos of the dead hawkfish.