Sinus infection spreading

[Dana09]

I purchased chickens at an auction. Golden comet, Rhode Island Red and black jersey giant. All big. Some I got are sick ( snot, rattle breathing, sneezing ). Some have watery stool. All chickens are together. I put 3 tablespoons of apple cider vinegar in their 3 gallon water. One passed (she didn't eat or drink). All are free range with a rooster i had before. Combs are red, three are laying, all eating, drinking and out sunning. BUT chickens that weren't sick are getting sick including my rooster! I gave them plain yogurt with probiotics once. I give them mealworms, black oil sunflower seed, laying pallets, apple cider vinegar in all water they get. Occasionally they get carrot peels, celery tops, and strawberry tops. I'm new to farm life and chicken raising. Should I purchased electrolytes, probiotics or something else to boost their immune system to fight the cold and keep the healthy ones healthy?? I'm new to farm life.. Any help is appreciated

 

[Wyorp Rock]

Sounds like some type of respiratory infection/illness.
Can you take them to a vet and have them tested?
Generally antibiotics would be used for treatment, but you really need to know which illness it is before you can successfully treat.
If you haven't done so, you should separate the sick birds, which may help the spread of illness but more than likely everyone has been exposed. In the future whenever you purchase new birds they should be quarantined approx. 30 days before introducing them to your existing flock.
There are several illnesses that have similar symptoms to what you describe, I have provided you a link - there is a symptom comparison chart at the bottom.
http://edis.ifas.ufl.edu/ps044

https://www.backyardchickens.com/t/12751/urgent-reminder-please-quarantine-newly-acquired-birds

 

[Dana09]

@Wyorp Rock
The chickens were separated but within the same coop. The new (sick) chicks didn't eat from the feeder but dug craters to the point I had to let them out or they would help themselves through the hole because they were looking for bugs. I will look into a vet in my area. Thank you.

 

[Wyorp Rock]

@Wyorp Rock
The chickens were separated but within the same coop. The new (sick) chicks didn't eat from the feeder but dug craters to the point I had to let them out or they would help themselves through the hole because they were looking for bugs. I will look into a vet in my area. Thank you.

They don't have to eat out of the same feeder for an illness to spread. Most illness/diseases are airborne and can be "shed" in dust, feathers, dander, etc. Even though they were separated, they were in the same general area as the healthy birds. Quarantine requires separate housing, preferably quite a distance away from one another.
I do hope you are able to find a vet that can assist you in finding out the cause of illness and that it can be treated successfully.