Best ascorbic acid (iron + copper stain removal) · Best for: Confirmed iron or copper stains (rust-brown, teal/blue-green, or purple-black). Ascorbic acid is the gold-standard reducer for metal oxide stains — it chemically reduces the oxidized metal back to a soluble form. 2 lb treats up to 20k gal. Must follow with a sequestrant to prevent restaining.
