what are these brown spots in my new inground pool (picture)

[Linzee8d]

Hello,
I have a newly built inground gunite pool since april this year.
starting one month after water fill, I am seeing few brown spots at the bottom and the side of the pool.
I have been checking /balancing chemistry per TFP method using the taylor K2006C test kit.
I followed the recommendation so balanced the water using the liquid chlorine for the 1st month and then switched to SWG pentair IC40.
So far I have six brown spots and they are all scattered. Their sizes are not getting bigger so far.


I took some photos.
Would this be rebar rusting thru? Should I contact my PB?
If it is just surface stain, what do i use to get rid of it? Thanks in advance!

POOL WATER CHEMISTRY RESULTS FROM THIS MORNING :
(I test the water myself with the Taylor K2006 kit, following the instructions.)

• FC : 10
• pH : 7.8
• TA : 70
• CH : 950 (it was high since the built from acid wash/CA city water)
• CYA : 70
• Boric Acid: 50
• Salt: 4800 (planning to drain out some water this weekend)

 

[Texas Splash]

Two things come to mind. Either rebar or tannin from something organic that fell in. Try rubbing a Vitamin C tablet on it now though to see if it's iron. Maybe place a magnet on there to see if it tries to grab metal. If not, then try sprinkling a little cal-hypo on it (organic).