Pool Stain Removal Guide: Metal, Organic, and Calcium Stains

Pool stains are almost always one of three things: metal (rust, copper, iron), organic (leaves, algae shadow), or mineral (calcium). Each has a specific fix — and using the wrong treatment makes the stain permanent.

Diagnosis first: the vitamin C test

Drop a crushed vitamin C tablet directly onto the stain. Watch for 30 seconds.

• Stain disappears under the tablet = metal stain (iron or copper)
• Stain doesn't budge = organic or mineral

Now try chlorine. Drop a chlorine tablet on a different stain spot.

• Stain lightens under the tablet = organic stain (leaves, worms, algae shadow)
• No change = mineral (calcium) stain or deep-set metal

Metal stain fix

Most common in South Florida well-water pools or pools topped off with hose water high in iron/copper.

1. Lower chlorine to under 1 ppm (chlorine oxidizes metals and locks stains permanently).
2. Add ascorbic acid (1 lb per 10,000 gal). Circulate 24 hours.
3. Add a sequestrant (like JackstheMagicPink or similar) to bind dissolved metals so they don't re-stain.
4. Slowly raise chlorine back to 2 ppm.

Organic stain fix

Usually leaves, palm fronds, or dead insects that sat too long.

• Brush the spot hard.
• Shock the pool to 10 ppm.
• For stubborn spots: direct chlorine tablet in a sock held over the stain for 30 minutes.

Calcium / mineral stain fix

White scale at the waterline is almost always calcium. Options:

• Pumice stone — for small areas (DIY)
• Glass bead blasting — for whole waterline (pro)
• Acid wash or chlorine bath — for heavy staining (pro)

Prevention

• Use sequestrant quarterly if your pool sees iron or copper
• Balance calcium hardness (250–400 ppm)
• Skim daily during leaf-drop season
• Don't let chlorine tablets sit on pool surfaces

Have a stubborn stain? We diagnose and treat stains — including acid wash for heavy cases.

Frequently Asked Questions