Recently, I noticed some brown spots on the floor of my pool. There a several of them, but not many.
They can't be brushed off, and do not grow (yet) either.
I have shocked my pool with FC15-17 last Sunday, and overnight is less than 0.5.
CYA: 40 (just replaced 2/3 water last Saturday.)
Borate: 0 (i guess, the test strips will be delivered tomorrow)
Any ideas about what they are and how to remove them?
Thank you in advance~