I've never used Melafix. So far, I have been very lucky with fish. Either they are healthy, jump out of the tank, or just disappear.
I'm wondering if your bottle of Melafix is old, or possibly wasn't stored correctly.
It seems odd that adding Chemipure made a difference.
I think I'd probably give up on the Melafix, and concentrate on getting your sick fish to eat. The best way I know to get a fish to eat is by offering it live food. We don't have many options available to us, so live means brine. Baby brine (yolk sack still attached) is far more nutritious, but not always easy to find. Get some live brine, and load it with Selcon. This should get him at least eating enough to sustain himself.
The Anthias is in a hospital tank now, right?