With all due respect, I have successfully treated blackhead multiple times with metronidazole. Blackhead has been confirmed by necropsy performed by me on a bird that did not survive. There were bullseye lesions on the liver which coupled with the sulfur-colored droppings provides evidence...
Looks like blackhead. Better round up some metronidazole quickly or you will lose the bird. You likely won't have time to order any, best to seek a vet or if you can find some metronidazole at a fish or pet store in your area. Fish zole or aqua zole is sold for fishtanks but it is simply...