Vitamin C is the cheapest fix for metal pool stains.

Start with vitamin C, but only if you’ve identified the metal first. Iron stains (brown/rust) respond well to ascorbic acid. Copper stains (green/blue) need a different approach.

Pour crushed vitamin C tablets directly into a sock and rub the stain. You’ll see it fade almost immediately if it’s iron. If nothing happens, you’re dealing with copper or manganese, which require a sequestering agent from the pool store.

Don’t raise chlorine levels before treating. Chlorine sets metal stains permanently. And go easy on plaster—scrubbing too hard damages the surface. Liner is more forgiving, but still don’t go ham.

One dose of ascorbic acid costs less than a hotel pool shock treatment and saves you calling a pro.