I repeat it again in 10 days. If the powder form of metronidazole you're buying is the 20% packs the dose is 1 tsp per gallon of water. I dose young birds with the powder form in their water. With older birds that require a higher dosage, I like to dose orally with tablets so you will have to...
Cayenne pepper doesn't work to treat blackhead in my experience. I had two birds die last summer while on cayenne. You need metronidazole, and if you don't start it soon you likely will lose the tom. I have treated birds with metronidazole only and have been successful if that's all you can...