Light brown stains from pool need suggestions

[SunnyOptimism]

Currently the following values are


FC 50
CC 0
TA 120
pH 7.2
CYA 20
CH 300
copper 0.2

Water is now clear.. but the stains are kinda coming back strangely. Under direct sunlight they look fine

https://www.flickr.com/photos/128250...posted-public/
https://www.flickr.com/photos/128250...posted-public/

but under shade there are browning maybe one would call copper stains.

I'm still confused by that FC number. Is it 50ppm or drops? If drops, then what samples size did you used, 10mL or 25mL?

There's a way you can determine what the stain is. You'll need a 3" trichlor tablet and a high concentration Vitamin C tablet. You put the trichlor tablet on the stain and if the stain lightens or disappears, then it is likely algae. If the trichlor tablet doesn't get rid of the stain, then try the Vitamin C tablet. If it lightens or disappears with application of the Vitamin C tablet then it is likely a metal (Cu or Fe). DO NOT LEAVE THE TABLET ON FOR A LONG PERIOD OF TIME AS THEY CAN ETCH A PLASTER SURFACE AND FADE VINYL.

If the stains are metals, then we'll have to run through an ascorbic acid treatment process.