Also, don't feel too badly about the tang. Sometimes, fish just die from unknown reasons (stress, handling prior to you receiving them). And never ever ever toss an almost dying fish from your QT into your DT (unless it was uber expensive or rare and you're pulling all the stops to try to save it). You only run the risk of contaminating the DT.
I don't care how "uber expensive" the QT fish is... not worth killing all your long time residents of the DT... even if they are damsels...