Vitamin C Stain in Plaster Pool

[Pltnsgt]

I had sever stains on my plaster pool and have tried shock and scrubbing it with a wire brush. I recently tried vitamin C in a small spot and it worked great. I then used it on a spot near the drain and I now have a black spot about 8 inches in diameter where the vitamin C was placed. How do I get rid of that spot? My pool is salt water generator, sand filter and the spot is at the 6 door spot.

Thanks!
Will

[Denniswiseman]

Try more vitamin C as it removes iron staining. I've never heard that ascorbic acid causes staining only the opposite
I had terrible iron staining and just added AA to the water and it cleared up well
Buy some powder online, put in a sock and rub over the area