You have to be 100% sure this is a bacterial infection and not viral. Even though you have seen symptoms that resemble this before (like and upper resp. infection, AKA URI)it may not be the same. Indiscrimnate use of livestock antibiotics, which this is, in cats and dogs is not a good thing. Using antibiotics like this is what causes resistant strains of bacteria to crop up and there is possible risk of infection to humans. I understand you do not have the $$ for a vet but please, please, please, seek the advice of a professional. What you got at the feed store is intended to use in livestock and chickens and such. I have used this in chickens in their water as you describe, I would never dream of giving it to my pets without veterinary supervision.