and people say Acanthurus tangs can't be kept in a environment with ichDave, your fish are now immune as long as they are fed correctly, not medicated and living in a stress free environment as much as possible.
If you would have medicated that fish, you would now be on the disease forum with all sorts of problems that the fish didn't have in the first place. I am not sure why so many people can't understand that as it is basic biology.
I put out there for years that anyone can come to my house and throw any fish into my tank with a disease of their choice and see if anything happens. No one applied.
Of course i didn't want a tuna or manta ray but a small fish that I didn't mind having.
A couple of months ago Humblefish came here and we went shopping for a fish or coral. I told him the same thing. Pick a sick fish and put it in my tank. We couldn't find one but I bought a coral from a filthy store where many of the fish were infected. I put that coral right into my tank and it is still there along with 5 or 6 other fish I got in that same store since then.
Immunity is the best thing there is and the more people learn about it, the easier this hobby will be.