Thanks for the reply. This morning I tried scrubbing a white splotch, after much effort, it lightened just a tad but is still there. It's as though it's part of the pool surface, like a rust stain would feel. It is completely smooth. I applied a descaler to it and scrubbed. I also applied 50/50 concentrations of m acid....no change! I am so disouraged.

I have a correction to make....my pool is ONLY 2 years old, not 3. Also, if it helps, I live in South Louisiana.

How do you suggest I apply the Vitamin C tabs? (I lowered the water level in the spa to expose/dry some of the staining.)

Thanks! This is consuming my time.

==========================================

I emailed some pics to you. Also, I just dropped a few C tabs in affected and non-affected area in the spa, which will be easier for me to monitor.

Thanks bunches!