I have used Melafix to help heal up shredded fins on certain cichlids that were being harassed(which it worked great)-unfortunately it seemed like the Melafix caused a mini-cycle(maybe it was just coincidental)in my 55g.
I love it for treating smaller things like fin wounds that need a little extra help to ward off infections or for persistent fin rot. I don't think that it would be as effective for something more extreme like Ich.