I haven't found GFO to be as dusty after it has been rinsed and I haven't noticed a link to it's use and the appearance of my regal tang.
About a year ago I had to qt all of my fish for ich. During that time my display was without fish for about 10 weeks and I had VERY large leafly macros and valonia growing in my tank. When the fish were returned I watched my regal, naso, achilles, and magnificent foxface eat every spec of algea in just under two days. This was equal to about 6 to 8 sheets of nori. I have since uped the amount of dried seaweed that I feed. 3 or 4 sheets a day.
I have found that very slowly (months) I am able to get new blue skin growing on the regal's face and new skin between the spines by keeping a higher temp of 82F, feeding the high amount of algea that I just described, and spectrum pellets, lots of PE mysis and smaller mysis, formula 1, and Pro Salt Pro V. I do soak one of the feedings a day in the usual stuff.
I wish I could say what makes the difference, but I can't. I have found that if I back off on feeding the new skin stops growing and if I release carbon dust into the system it quickly gets worse.