Thanks for your feedback.

Yes, I do inspect the cell periodically. No problems there.

As I mentioned, the stains first appear on the steps. There is a return in the steps and the steps are white, which is probably why I notice it there first.

I'll see if I can find water quality info on our city water.

I take it a passing bucket test for metals doesn't necessarily mean the water has no metals, perhaps just a low level of metals? When I did the bucket test there was absolutely no staining/discoloration in the bucket.

I do stick with "pool salt" that says "no additives". I do not use water softener salt.