Juvi's of many species will play well together, even species of the same, When certain individuals mature, angst can start.
Where is the yellow head going, those usually get pretty nasty when mature, If they are to be kept with fish, it needs to be a large tank that can handle such fish as triggers and large angels, many tangs aren't even safe with a mature yellow head.
Have you thought about reintroducing a pvc, maybe it is an irritation from the rocks and substrate that's causing it. I forget the diameter of the pvc I used, it does have to be large enough, but the ribbon doesn;t need too huge. But they literally have to be able to turn around in it. Eels are contortionist so it isn't as bad as it sounds.