Tylan injectable worked for CRD for me, and quick
As Kat says they feel better usually the next day
I used a 22 ga. Needle
Tetracycline did not even touch it, maybe masked symptoms.
Tetracycline in the water will have to be made fresh everyday, or ineffective.
I would be treating the other birds with it maybe if they responded to it and depending on how many birds you have to treat.
Don't treat the others if they aren't sick. If they do get sick, treat with Tylan.