Hello...Looking for some help. I have a large pluco that is around 3-5 years old. He has always been healthy survived anything in the tank that killed other fish. The other day I noticed that he has some fairly large discoloration marks on him that none of the other fish have. I thought that it might be ick so I treated the tank, but he still has the spots. I have no idea what it is or how to help him. We would hate to lose this fish, he is our fav. Thanks!