Many people struggle with stains, so I thought I'd take advantage of the fact that I accidentally added well water instead of softened to my fountain as an opportunity for a visual demo
When iron or copper are oxidized via elevated chlorine levels, which is what happened in pic #1 at raw well level of 2 ppm iron, that's what you get. Add enough HEDP metal sequestrant (I used Metal Magic by proteam, a few ounces) and the second picture is the SAME water.
But it wears off, which is why you need to maintain it
Hoping to be helpful.