Brown stains gunite pool

[raiderron]

1 year old gunite pool. Northern California city of Willows water. Scattered, (some large) brownish stains. Contacted pool builder numerous times, (each time I get a different idea / direction) stains persist. I treatred and maintence treat for algae, used stain remover, kepping pH < 7.1, etc. Sanded stained area's and some areas the brown stain sands off, ( sanding leaves a light gray color) but some area's it doesn't sand off, and some new area's starting to stain. Water tests are negative for metals, algae etc. However phosphrus is very high, off scale, but Pool builder says high phosphforus not causing stains. No one seems to know what to do! HELP!

[geeman]

Is this white marble plaster? Have you used any fertilizer for the grass recently or ever?

[raiderron]

Thanks for the reply: White gunite, not sure what a marble finish is, so I think no. Yes I do use fertilizer, and yes some fertilizer may have gotten in pool, resulting in off the scale phosphrus levels. Could this phosphrus level be the source of staining? I have used phosphrus remover 2 times, I will check level tomorrow. ... At this point I have been told by my pool contracter, "you could pay a scuba diver to sand the pool". Could really use some advice, again thanks.