There's a fungus amongus

[Delphinus]

This probably doesn't help much, but when I bought my percs/ocellaris back several years ago now, one of them developed a small patch of fungus. It (the fungus like growth, that is) disappeared within a few weeks, and that fish is still with me.

I'd for sure do as you suggest ... keep the fish well fed, vitamins, anything you can do to promote "good overall health" and I'm sure it will get better.

Good luck!

PS. I have no idea if it really was "fungus" or something else. I call it fungus, because that's what it looked like. Like a small piece of cream cheese or something. It was on the body just aft of the pect fins. But I doubt it was "really" fungus but in fact something else. Sorry I can't be of better assistance other than to offer "moral support" ....