I'd heard that melafix could be used on anything because it was a stress-reducer, and that it couldn't really be overdosed because it was organic or whatever. Well, I used it because my fish were flicking, and less than the full dose just in case. The next day my ghost knife was dead, no scratches, no sunkenness, just dead. We dosed again with both pima and mela and the next day my multipunctatus was dead, looking very pale so you could tell he was dead.
My lfs told me it was definitely the melafix that killed them, and that its made from melaleuca (tea tree oil) which is toxic to many animals. It causes the fish to create a thicker slime coat on themselves, because its toxic, which in turn protects them from other nasty things. Salt does this too, btw, and thats all I'll use from now on.