Discoloration on pool floor

[Wizaugh]

Pool is getting better/clearer. There is some discoloration in the deep end (left side of pic, the white circle is the drain) that won't come off with a brush. I don't know if it's paint peeling or some sort of stain? Sorry, but this is the best picture I have at the moment.


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Any ideas?

 

[Butterfly]

Try holding a trichlor puck on the stain for a couple mins to see if it lightens.

If no results from the puck, try crushing some cheap vitamin C tablets in a sock and hold the sock on the stain for a couple minutes.