marine velvet, ideas please

I was helping a buddy with his tank the other day because he just recently lost a clown fish. As i was looking over his other livestock (which isn't much) I noticed his other clown fish diving at the sand and rubbing against it.



I came back 2 days later and noticed his clown fish had a white like hue to him kinda like a moldy look. Right away i pointed it towards marine velvet.



So we have some questions or opinions for what we should do.



This is his main tank which is 75 gallons. It is a reef tank with rock and sand. Obviously we can't dose with copper cause of corals.



His first question is if we move his corals to my tank how long does the copper treatment stay in the tank. So if he does a copper treatment for 2 months how much longer after the 2 months does the copper reside in the water?



Would he have to remove the rock and sand? Does the copper store within all of it??





Is a better option to create another tank and put his 5 fish in that and copper dose that tank??



Just looking for ideas because it is a very bad situation and i am trying to help the best i can...



I have removed his butterfly fish because it had been rubbing against the rocks and was very discolored for 2 days straight. I put her into my QT tank and i ordered some copper stuff to add to my QT cause there is no sand or rock in it.



I was going to try to catch one of his damsels (he has 2) but couldn't. It looked as though 1 damsel had a white patch near face that wasn't like a ich spot more like a mold spot or a wound.



4 fish still in his tank.



Please give me some ideas, he is very discouraged because his corals are looking very impressive then he gets velvet...