I explained to the vet about being recommended to that I not add anything to the chickens water like vitamins and probiotics because it can be too much. So; just before this happened, I didn't add anything to their water for about 2 weeks. We had a fair amount of rain in that time.
She said its really all about the environment the chickens are kept in when it comes to their health. There are pros and cons of both free range and run kept chickens.
She told me that it does not take long for their little bodies to be overrun with bad bacteria especially if they are not on a quality feed or have things they need added to their water.
What I used to do was set up three waterers. One fresh; one with vitamins and one with probiotics. I let the chickens decide what they needed. I am going back to that.
She told me that probiotics multiple times a week was not bad. Just offer them some plain water as well.
I am aggravated with myself.