Alve,
Ahhh, I was afraid of that - the lesion goes all the way through the fish. It looks like a bacterial plaque infecting the site of an injury to me.
Saprolegnea fungus DOES NOT LIVE in saltwater - in fact, one of the best cures for it in FW fish is a mild salt solution. There are some marine fungus problems, but most of them, like Ichthyophonus, are internal, and not sapprophytes. Forget the garlic and vitamins, there is absolutely no indication that these will have any affect on a serious issue such as this.
I'm afraid that it looks like this infection is on the verge of becoming systemic (spreading throughout the fish). There is nothing to be done if that happens, but it is unlikely to affect any of your other fish. The only suggestion I would have would be to move the fish to a QT and treat with a broad spectrum gram negative antibiotic with low toxicity such as neomycin.
JHemdal