When you say "a touch" of copper sulfate, what kind of dilution do you mean? Roughly how many crystals of copper sulfate per gallon? Can you use it safely in those galvanized water founts?
I honestly don't know about the galvanized metal dispensers because I don't use them.
The Copper Sulfate I use is a fine powder, much like sugar. I use just shy of a 1/4 tsp per gallon of water for a single preventative treatment, or approximately 1/2 TBSP per 5 gallons if I already see signs of distress in the flock. Once they've consumed all of the treated water I switch back to plain, fresh water. After 24 hours I add extra probiotics to their feed to build up the good intestinal bacteria since copper sulfate can kill off the good as well as the bad. They get three days of probiotic enriched feed. After that they only need a "booster" of probiotic feed approximately every two weeks AFTER at least one day of receiving ACV in their water. (Don't use ACV at the same time as probiotics as the acid in the vinegar can actually kill the beneficial bacteria before it reaches the gut.)