Start with a stain ID kit and use ascorbic acid for metal stains.

Yes, you can remove stains from pool plaster — but don’t just pour in muriatic acid and hope for the best. That’s how you etch the plaster and make things worse.

Most stains are metals (iron, copper, manganese) or organics (leaves, algae, pollen). Metal stains respond to a reducing agent like ascorbic acid (vitamin C). Organics are usually handled by a good shock treatment or a stain-specific enzyme. Get a simple stain test kit first — it’s cheap and saves you from guessing wrong.

For metal stains: turn off the pump, broadcast powdered ascorbic acid directly over the stain, wait 15 minutes, then brush. If it fades, you’re golden. If not, it’s likely organic or calcium scaling, which needs a different approach (low pH for scaling, high chlorine for organics).

One warning: never use a copper-based algaecide if you already have copper stains — it’s like pouring fuel on a fire. And test your source water for metals before refilling.

A little patience and the right chemical saves you from having to replaster early.