Hi... May I suggest you use the SEARCH here on the website... Search the symptoms and you will get links to answers, threads. Watch for other symptoms in the chickens, check their poop.
What antibiotic did you give? Tetracyline (Duran 10) is given at 1 teaspoon per gallon of water... as much as all your chickens will drink in 24 hours, change the water and re-dose until three days after symptoms are gone or seven days, I believe.
There are stronger antibiotics, injectable ones... you can get Tylan 50, syringes and needles at the feed store..... there are instructions for giving injectables or oral antibiotics here on BYC. And, there are oral ones that you give to one chicken at a time individually... search "giving oral medications". You can't be sure a sick chicken get enough medicine (via drinking water) as they very often stop drinking and eating if they are really sick. This is why individual injectable or oral work better.
You will find that people here are willing to help... giving more information is better... such as how old are the chickens, how long have you had them? Have you ever wormed them? With what? What do you feed them? Did you check for mites? Have you added any new chickens to the flock? Did you keep those new chickens isolated from the flock to see if they were sick at all before introducing them to the flock? A flock with a worm or parasite problem will display many symptoms, symptoms and death that you would not think could be from having lice, mites, worms, etc.... but, it's possible.
You won't know if your chickens are "carriers" until you know what the problem is... what the illness is. Some things are "carried", some are not. (From what I have read here on BYC).
There is an eyeworm... there is are threads about it.. here's one:
https://www.backyardchickens.com/forum/viewtopic.php?id=95554
I do not know much about all this... I am repeating what I have read here or been told. You can find more experienced information here. You can count on good, accurate info from dawg53 if he posts a response. Many feed stores carry anything you might need to treat your chickens, and most are open on Sundays as well.
Use the search here on BYC for more and better infomation. Good luck.
