Since chickens carry it I recommend putting a medicine/wormer that Will kill blackhead in everyone feed. I've heard live apple cider vinegar in the water can ward off this disease. Good luck.
I had the same problem last year & lost a young beautiful bronze/Spanish cross Tom. Since then I've started clipping wings & trained them to go in the coup at night. There is a heat lamp & plenty of nesting material. They can still get up high & snuggle in a nesting box. Now I just go out @...
I have my flock mixed but I always worm & vaccinate & quarantine a new bird before it goes in the mix. I also know that the soil they are on hasn't had other fowl on it in several years. Hope that helps.