cthetoy, so sorry to hear that. Best of luck on the next one. I think the Q-tank, with treatment, nonetheless, was a wise decision.
I know this is a PITA, but next time I quarentine a difficult species I am going to age the Q-tank. I think it's best to age the water in the hyposalinity/copper tank before adding the difficult fish. I prefer hyposalinity. In my case, I am going to need 2 tanks plus an aging RO water tank/container. I am going to age a hyposalinity tank with some base rock, strong circulation, and no fish for at least a month with a salinity of 1.009. I will wait for some nice algae to develop to help keep the pH up and give the fish something to graze on. I will throw in a nitrogen source to spike the NO3 cycle and develop nitrosomas fauna over the month. When this is established, I will buy the difficult fish and place it in a different tank (tank#2), Tank #2 will be pretty bland with some pvc (I don't want a NH3 spike while I drop the salinity). Keep in mind that tank #2 will be set up for some time, as well, before buying the fish. I will use my litermeter to continually and slowly drop the salinity in tank #2 (it will start at 1.023/4/5) over 3 days with aged, highly oxygenated, RO water (kept in a seperate tank). I will also have a skimmer on both tanks to keep the tanks highly oxygenated. When the salinity in tank #2 is finally decreased to 1.009, then I will transfer the fish to the aged hyposalinity tank (tank#1) and keep him there for 30+ days. I will then slowly raise the salinity of tank #1 back to 1.023-5 over 7-10 days. Then the fish goes into the display tank. If you have the room to do this, I bet it would work great. My aged hyposalinity tank is going to be 75 gallons.