Orange Shoulder tang; disease, or natural change?

[FishFun]

Mine is in the middle of changing, I wouldnt worry about his colour changing to young, its normal for them to change a bit when stressd, mad or scared. Its just a reaction to something. All my tangs do it, my regal's black stripe turns gray when shes ticked. I would not worry. I will try get some pictures latter. As for tank size a 30g is ok for now, as long as it has a really good hiding spot. Mine has its own spot as well as the others so you should make sure he has a place to call home