Teila...
I was worried when I used copper sulphate on the hen in question.. thinking I'd get the dosage wrong and kill her as a result but it didn't do her any harm (that I am aware of) nor did it harm the canker either :/
I haven't decided yet if I'm going to dose the others but if I do it wouldn't be a regular thing because I'd prefer not to use chemicals either but maybe good for the short term just to make sure no other outbreaks happen since it's always a possibility while there's one around carrying it.
Copper Sulphate can build up and poison. Horses need it in Aust due to too much fertilizer used on our grass but it MUST be balanced with good calcite from Commetcial Minerals. The calcite eables the digestive system to get rid of the copper.
When I got troubled horses to fix first thing I did was feed Local Seaweed meal, and dolomite, raw apple cider vinegar and a trace of copper sulphate. Not a single horse did not calm right down inside a week.....but chooks????? Mmmmmmmmm set me to thinking about my own chooks