Good morning, Straight6tt.
I know your set up is entirely new, but have you checked the water coming out of the returns to see if its clear or cloudy?
That Slimebag I mentioned before that some people use to reduce metal content might also double to help as a filter aid...they sell an adapter to fit it over a return. I don't own one myself, but have seen several favorable reports. (
The Slime Bag | The Easiest Way To Maintain Crystal Clear Pool Water. )
Then again, time, IME, is all a sand filter usually needs

I just know you're anxious to clear and enjoy your new pool.
P.s. re toilets...my toilets use softened water that has about .3 to .5 ppm iron left in it after treatment, and they are not stained. But that level in a pool CAN and WILL stain if ph is high, high chlorine is added etc. without sequestrant. With the purple endpoint in the CH test AND the first clear and immediate green, I don't think there's any question about the presence of metal