The condition affects mostly Tangs. It is because their mucous coating is rather thin and of a slightly different composition. Other fish, e.g., the Angelfish, can be affected if their mucous coating has been compromised. There are minor variances in the fish even within the same species and/or family. There are no guarantees or rhyme nor reason why some fish succumb to this and others may not. Quite often it can be combined with additional stressors. For instance, if the water quality is not top notch, then it may be a contributing factor.
Grounding pole will work IF it is properly set up. Also, I have heard that even though there may be a ground, there still may be some current present. I'm not sure of this, though. I also don't know how to verify that there is no current in the aquarium. Perhaps someone else has a way to verify this.
Although there may have never been any copper put into the tank it doesn't mean there isn't copper there. Copper can come from the water the fish came in. E.g., many fish suppliers use copper in their system to keep parasites at bay long enough to sell their fish. Also, copper can leech into the aquarium through rocks and/or metals in contact with the water. Some dry salt formulas in the past have also contained copper. Still worth checking the water for it.
Regarding nori: Is it sun or air dried nori? If it has been baked like for sushi, its nutritional value is reduced. Check this out. This is covered in the nutrition link. I would replace the nori with actual sun dried seaweeds readily available at most fish stores that sell ornamental marine fish. Also, very important, the link explains how much nori/seaweed is the right amount to feed.
y and has been adding trace elements. Has perfect naso, copperband, 2 perculas, and hawfish for at least 2.5 years. Proble 4 fish Koran, Sailfin, Flagfin, and Hippo have l
ost slowly all color in face actually became albino. Other then this they are fine. Sending pictures. Any help on what this might be. Added grounding assembly also thinking maybe low voltage. Thanks for any help 
