You treat Blackhead with Metronidazole (hope it's spelt right) 250 or 500mg from your vet, if 250mg 4 tablets to 1 gallon of water if 500mg 2 tablets to 1 gallon of water changing water everday for 3 to 4 days then repeat 7 to 10 days later.
Peachicks and Poults are about the same to raise.
Ricky