Tylan power and injections

[toastymornings]

Hi,
I have a flock of 20. 2 are obviously ill, the others are not showing obvious signs but should I treat them as well because if two are sick they may all end up getting sick since they are together? I ordered both the Tylan Powder and the injections. Which should I administer? The powder is placed into their waterer for everybody. If someone is not sick yet will treating them hurt them? My idea was to inject the ones who are obviously sick and just give the powder via water for everyone else. Does this sound like a good idea? Now if I did do that, and the ones I injected drank the water, would I be "overdosing" them?

Thank you for any responses.

 

[Kiki]

When you say 2 are sick, what are their symptoms?
What does their poop look like and
How long have they been showing these symptoms?