welcome to the forum, the both of you
Wasting disease is not really a disease, but a collection of symptoms. It may be, it may not be. I would see about treating for internal parasites - I don't know what else to suggest.
Inverts are not susceptible to fish diseases, and vice versa. There...
They've shown up and disappeared on fish's fins occasionally. That's the new sev - it had the spot when I bought it, though it was a little bigger. I've never observed it to have any affect on anything. Obviously as the fish is in the show tank