Sick Flame Angel

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My Flame Angel has become sick and I'm not sure what the cause is or how to treat him. He has stopped eating and his colors on his side have drastically faded. He was flashing off of the rocks but I couldn't see any external parasites. He doesn't have any lesions. I tested the water and there aren't any problems. I have General Cure, Ich X and Pimafix on hand. I also have Kent garlic and Selcon that I use on my fishes food daily. I have heard that adding a directly to the water can be beneficial as well. I will start him on the General Cure tonight. Any other suggestions on what I should use or buy? He is in my isolation tank now.

Any help would be greatly appreciated.