Lethargic, sticky nostrils, comb/waddles changing colors

5 French Black Copper Marans- 3 cocks and 2 pullets bought at 2 months old, fed with starter feed. At 3 months a pullet and cock started became lethargic, had sticky substance on nostrils and beak, and combs went from red to gray in about a week. Administered Sulphebalzan Sodium to water for 5 days tapering off the last 2. They both died. A month later another cock came down with the same symptoms and died. I sterilized the coop with half chlorox and half water and let it sit for a couple of days. My last cock is now demonstrating the same symptoms at 18 weeks old. I hate to lose another of these beautiful birds. Would love to know if anyone out there has any experience dealing with these symptoms and what it might be?