Help me please, I'm confused.

I’ve serviced a pool with iron staining on the pebbletec and baskets similar to yours. Fill water was city fill and the water tested with zero iron. The best assumption I could come up with was tainted salt that caused the iron contamination/staining. What salt have you used in the history of the pool?
 
Update- more confused than ever. Pool is looking much better and I’m not sure why. I added polyfill to skimmer 24 hours ago it’s still snowy white, didn’t pick up any iron. I haven’t added a thing to the pool in 48 hours. All I’ve done is backwash (brown) once a day, brush and vacuum with robot.
Tuesday night, started SLAM with two more gallons bleach.
Tuesday night FC 18
Wed morning FC 17.5
Wed night FC 17
Thursday morning 17
Thursday night 16.5.
Never had CC at all. Never added any more bleach. I’m glad it’s better but wish I understood more what is happening.
 

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I’ve serviced a pool with iron staining on the pebbletec and baskets similar to yours. Fill water was city fill and the water tested with zero iron. The best assumption I could come up with was tainted salt that caused the iron contamination/staining. What salt have you used in the history of the pool?
I confess I just buy whatever salt they are selling at Lowe’s the week I need some.