The Dietary Supplements thing is a minefield, I'll say that. I agree with the other post about how good diet can be a tool to promote health/ward off trouble.
But what I wonder is in particular the issue of natural fish diet vs captive. For example, I have a Foxface Rabbitfish that for a long time refused to take any algae. It does now. It is supposedly omnivorous with some preference for algae. I've not found much written about what happens to fish when not fed their natural diet. The Foxface now eats algae and frozen so it's getting what I think is close to its natural diet.
But what I wonder is in particular the issue of natural fish diet vs captive. For example, I have a Foxface Rabbitfish that for a long time refused to take any algae. It does now. It is supposedly omnivorous with some preference for algae. I've not found much written about what happens to fish when not fed their natural diet. The Foxface now eats algae and frozen so it's getting what I think is close to its natural diet.