In groung pool rectangular, 32 feet by 15 feet, 2-1/2 foot to 5-1/2 foot deep , 11 foot spa with water fall, salt water, chlorine gen, approx 13.5k gallons. Pool is 14 years old, I have owned it since 2016, Location Charlotte NC
Uncovered the pool in April, water looked good/actually great,. couple of worms and leaves got into the pool under the cover during the winter. Cleaned the pool filled to normal level, put in two lbs shock , ran for two days took water sample down to local pool store had water tested, results perfect.
Plaster has stains, some dark some barley noticable, appearance anwhere from light gray /brown/black to very black. Have tried most/all of the recommended remedies from various pool stores etc etc. The stains cannot be removed by brushing. They appear to be ingrained in the plaster which is light blue.
Is my only recourse to drain the pool and have it acid washed, and if so what do I do to keep the stains from returning.
Thanks in advance for any advice