Vitamin C is your first bet for pool rust.

Yes, you can remove rust stains from a concrete pool without draining it — and you don’t need harsh chemicals for most cases.

For light surface stains, grab a few vitamin C tablets (the cheap, unflavored ones). Rub them directly on the stain underwater. The ascorbic acid reacts with the rust and dissolves it in seconds. Works like magic for typical metal marks from hairpins, tools, or furniture.

For tougher stains — deep orange or brown from iron in your water or pool finish — step up to oxalic acid. You can buy it as a powder (often sold as wood bleach or pool stain remover). Dissolve a small amount in a bucket of water, brush it on the stain, let it sit a minute, then scrub. Rinse well. Both methods are safe for concrete and won’t damage plaster or tile if you don’t leave them on for hours.

One warning: don’t use muriatic acid unless you really know what you’re doing. It’s aggressive and can etch the surface if you get the dilution wrong. Start with vitamin C — it costs pennies and avoids the headache.

Test any method on a small hidden spot first. Concrete is porous, and some finishes react differently.