Runny nose with no other symptoms!

[annabanana25]

I have two chickens, one around 12 weeks and the other 7 or 8 weeks old. They always have a runny nose that comes and goes with no other symptoms. I think it’s contagious because I got the older one a chick to keep her company and now they both have runny nostrils. It’s clear and kind of stinks. They have great appetites and don’t act sick. I did give them a round of antibiotics (baytril) thinking it was possibly mycoplasma or coryza or some respiratory infection but it didn’t clear up. They eat all flock feed with 20% protein and they get apple cider vinegar in their water along with oregano, red pepper flakes and garlic in their food. I don’t think it’s environmental. Any ideas on what it could be? It is really hot here (we live in MS) and they drink water constantly.