Everything is a learning experience. One thing that might be advisable, nothing to do with the dead fish, is to set your temperature a little higher between 79 and 80. Ironically, about 8 years ago, I had a suicidal clown in a pair that I had and in a moment of weakness I liberated a Petco clown. I didn't QT at the time and acquired marine ick as as a result. I did copper treatment in a quickly bought QT and they survive until today. I did learn at the time that the higher temperatures (and QT) ward of the ickies.