Stains from dirt getting in pool

[basod]

That means it is an organic stain. Raise your FC to shock level for your CYA or a little lower and brush daily. That should help reduce/remove the stains. [FC/CYA][/FC/CYA]

if the puck was left overnight(bad idea) and lightened the stain, it could be the CYA acid removing the stain.

This may be a unique situation as the soil is adjacent to the pool, and could be contaminated with rebar oxidation.

I'd try the vitamin C test and if does nothing then assume its organic.