Have started to have staining in my 2 yr old SWG pool (Sunstone finish). Stains are either dime sized or 1-2 inch streaks. Have tried both scrubbing with the lemon/Vit C tab and with a chlorine puck. Strangely have not noticed much difference with either. Pic is attached.
FC - 5 ppm
CYA - 45 (but raising to 80 today)
ph - 7.5
Any ideas if metallic or organic stain? Then course forward?