Just recently I started noticing these rust colored areas at the bottom of the pool. As of now I would say I have around 8 or so. I have tried brushing them away but do not come off.
Anyone know what this might be and what I can do to get rid of them?
BTW, my pool is IG, 15,0000 Gal, Salt water, plaster.
My PH is at 7.8 (we have had a bit of rain lately, so just treated with Muriatic Acid to lower PH), CL is at about 5 ( just ran a full 100% chlorine session for about 13 hrs on the CL generator yesterday), HRD 350, CYA 20, ALK 80
Here is a pic.
Any guidance would be greatly appreciated.