One of my cardinals has this black area on one side. He seems to be fine otherwise, and hasn't lost any color. However he isn't sticking around the other cardinals very much... Hopefully someone can tell me by looking at this picture I took. Thanks!
No idea. Sweet slate though.
I don't see anything on my other cardinals, should I think about euthanizing the one...? Or wait it out?
I'd personally wait until you see more symptoms, the other fish have already been exposed at this point so need to euthanize anyone yet. Keep the water clean and hope we are both wrong!