Help! Baby chicks sick!!

[sezua]

I have three week old chicks and one is sick with cough and getting bubbly nose. I have tried everything and now had to resort to antibiotics. Still no progress after a week of using oxytet and now another is coughing. I am going to separate them today but, I wonder if it's to late and the others will eventually get this. What else can I do? I have also been given so much different advice to how much oxytet I'm supposed to be given them..How resilient are baby chicks with being able to get over this stuff whatever it is? I have done vet rx, raw garlic, electrolytes, nutridrench you name it I am giving it to them!