Ascorbic acid works for most metal pool stains.

Yes, a vitamin C treatment (ascorbic acid) is the standard fix for iron and copper stains on pool plaster or vinyl.

You lower the pH to around 7.0, then broadcast ascorbic acid over the stain area. It reacts quickly — you’ll see the stain fade or disappear within minutes. For stubborn copper stains, you might need to follow up with a stain-removing sequestrant like Metal-Free or a