Drained and cleaned my pool last month (2nd time in 15 years) and tried to remove several stain spots with muriatic acid to no avail. Filled pool and brought chemicals back to normal. This is the first time I've had stains. I've fought black and green algae successfully, but this stuff stumps me. The gunite looks and feels ok (a little rough), but the brownish stains are disfiguring. Thanks for any suggestions!
