From this picture, this one looks a little beat up, with the marks on the body (possibly from a net?). Has it been flashing, rubbing itself against objects? Does it eat as well as the rest? It does look thin. If it got those marks from flashing, it could have a few flukes, and a treatment of Prazi Pro usually clears those up. Good luck with them. I'm also growing out some monos, so I'll look forward to seeing your new tank setup.