Pictures of everything would help. If you take them, send them -- full size! -- to poolforum AT gmail DOT com or poolforum.pics AT gmail DOT com.

We don't have recommended chlorine levels IF you actually have metals (Cu &/or Ag) in your pool water. Mineral cartridges come in two types: those that are worthless, because they do nothing, and those that are WORSE than worthless because they put uncontrolled and unpredictable amounts of metals in your water.

I'm you might try Iron Out, but I'm not sure that it would remove silver, if that's what the stain is.

If you can report models and mfgs on the mineral unit and the ozone unit that would help.

Ben