copper reactivity

Hello:

I have copper-colored staining in my shower and sink basins, but not in my toilets. I have low pH shallow well water near a wetland. My one year old copper pipes are grounded. I have a water softener. Why don't I have this problem with the toilets? Is is related to the fact that there's no hot water supply to them, and if so why does that make a difference? I changed out the copper flex pipes that supply and exit the water heater, because I heard that soft copper will more readily corrode in a low pH environment. This hasn't solved my problem. Thank you