What is this on my Bartletts

[Jcj0033]

I have about 10 Bartletts they were all doing fine in my qt tank and then all of a sudden they look terrible !! 1 died and 4 others look like this !! I have copper in the qt but it looks like uronema !! I don’t know what to do but I need to do something quick !!
Any suggestions ?

 

[Sniperhank]

Do a large water change. I'd suspect to see some sort of ammonia or another nasty parameter.