I have a Blue Hippo Tang and he always rubs on the coral too. Just on his very bottom of his body. He does not do this all the time but sometimes if you stay out of sight he will do it. He does not do it if he knows someone is watching. I have been watching for any changes too. I have not noticed any. He is swimming and staying active. And he eats normally. I did have a sick Clarkii that died this morning so I have really been watching the others. I put the Clarkii in a QT
tank so I hope I kept the others safe. I think the Clarkii came with (clownfish disease) from the store. I only had him short of a week when he became slimy and white. I put him in a QT
tank with Formalin but I could not save him. The tank has been running since June. Things have been fine except for the Clarkii. Do any of you trust or use online fish stores??? We only have one store here and I am not happy with them.