Pool is 20 years old in ground fiberglass with salt and a sand filter. Pool is 11500 gallons levels are
FC 10
TC 10
ALk 120
PH 7.8
TH 250
CYA 50
Salt 3000
Water is very clear and sparkly
Had tested for metals at pool store and none present according to them
Tried ascorbic acid on spots. Rubbed...