Desert Rooster is correct. Sulmet can be used to treat coryza as well as gallimycin, aureomycin...soluables mixed in water. How do you know if it's coryza? You can tell if it's coryza if there's a foul odor about the nostrils and/or head area on your silkies. No smelly odor means it's something else, possibly mycoplasma gallisepticum (MG.) Tylan 50 injectable can be used to treat MG, but not coryza...it would be most likely be ineffective. If in fact it's MG, it would be best to treat your silkies with denagard. Denagard will clear it up and there's no resistance nor withdrawal. You will have to give them a preventative dose of denagard once a month. It would be better than injecting them with tylan in which the disease will eventually build resistance to the tylan, then you'd have to use something more powerful. As I stated, there's NO resistance to denagard and a bottle of it will last you a long time. Type "denagard" in the BYC search box and read up on it if you wish. If it's coryza, use sulmet and follow the directions on the bottle or package. Sulmet is harsh on their system and I recommend that you feed them scrambled egg mixed with buttermilk (not yogurt) during the sulmet treatment and a few days after treatment. Do not mix anything else in the sulmet treated water.