I have a 16x32 gunite pool, 6.5ft deep end, 6 years old and converted from chlorine to pentair salt generator 2 years ago. I originally questioned pool company about some rust colored stains that appeared over last year that looked like a hair bobby-pin had been left on bottom and rusted, but there is hasn't been anything dropped in pool to rust. My pool is crystal clear, I have had some varying darker and lighter areas in deep end over the last few years. Now I have some in 3 of the rust looking stains different places in my pool about 2 inches long each and some of them are in a V pattern with each side about 1-2 inches. Pool installer hasn't seen them in person, I did show photos and said it was either black algae or deposits from calcium/minerals and I needed to drop water level and replace to lower calcium. Calcium was 350 mid week and I drained it 5 inches and refilled as was instructed now level is 380 today. They told me to drop/replace water again today and recheck Monday. Every other level checked was within normal limits except calcium. 6 years and I've never been told to lower water and replace, not convinced this will help and wonder if my well water my be raising it. Told me to try stain free on the rust looking spots, haven't done that yet. Any suggestions/ comments would be greatly apprecitated. Let me know if there is any other info that may be needed about my pool, wish there was a way to post images of the stain to see what people think they are.