I QT all my new arrivals for observation I also add salt and heat tank to 86 degree's for initial treatment and I keep feeders from another QT tank readily available for them to eat when wanted, in worse cases I add meds if needed most of the time not even needed. I also do 40% water changes daily redose salt. Once they are eating well and have no torn fins then transfered into the growout tank. Seems to work well bottom line these fish are expensive and it sucks to loose them for whatever reason. I am sorry for your loss.