Thanks ! Here's another pic, yes they are tetras (glofish) , here's a shot with a normal one and the sick guy in front. you can see his gills are opened and whole head area is swollen. Don't know what to do, he's has been that like a little while I am afraid- but looks like it's getting worse.
This would keep the fish in suffering, best to euthanise it.Have you tried treating it with General Cure? I have a Mollie that had something around her mouth that I treated with a Fungus Cure & then a General Cure. She’s in good shape now. I treated her with her tank mates as a precaution not knowing it they were infected.