Help, sick fish maybe?

[wookie]

Here's the sole Mono remaining. You can see something going on badly with his skin. The other ones progressed like this - but never as bad. I think they died before it got that ugly.

Sigh . . . . I'm thinking this will be the end of my aquarist days... The GF is choked/sad about how much time has gone into this and money and of course losing the nice fish, only to have this happen and pretty much nothing we can do but watch.