Pool stain treatment chemicals and brush on a daylight deck

How to Identify and Remove Pool Stains

Removing pool stains starts with the right diagnosis — metal, organic, calcium, or algae each respond to different treatments. Here’s the step-by-step for removing each type without making things worse.

Step 1: Identify the stain type

Hold a vitamin C tablet against the stain for 30 seconds underwater. If the stain fades visibly, it’s a metal stain. If no change:

  • Drop a chlorine puck or shock granules on the stain underwater. If it lightens, it’s organic or algae.
  • If no change to either test, it’s a calcium or mineral deposit.

Step 2: Treat the specific type

Metal stains (iron, copper, manganese)

1Balance pool chemistry first (pH 7.4–7.6, low chlorine if possible).
2Add a metal sequestrant per the label rate.
3For visible stains, apply ascorbic acid powder directly to the spot — sprinkle through a sock attached to a pole or pour onto small spots from a cup. Brush in.
4Run pump 24/7 for 48 hours.

Organic stains (leaves, acorns)

1Shock to 10–15 ppm free chlorine.
2Brush the stain vigorously.
3Run pump 24/7 until cleared.

Algae stains (residual)

1Triple-shock to 15–20 ppm.
2Brush daily for 5–7 days.
3Add an algaecide labeled for the algae type you’re fighting.

Calcium scale

1Lower pH to 7.2–7.4 with pH Down.
2For visible tile-line scale, brush with a stainless brush and tile-cleaner gel (citric acid based).
3Maintain calcium hardness at 200–400 ppm to prevent recurrence.

Chemicals and tools

Durachlor pool shock for organic and algae stains

Durachlor Assault 73 Shock

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Durachlor pH Down for scale prevention

Durachlor pH Down Reducer

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Pentair 18 inch stainless algae brush for stain removal

Pentair 18″ Stainless Algae Brush

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If the stain won’t come out

Stubborn stains, especially on plaster after several years of neglect, sometimes need a full acid wash by a service tech (drain the pool, apply diluted muriatic acid to surfaces, neutralize, refill). This is a major undertaking — budget $400–$1,500 depending on pool size. Reach out to PST Pool Supplies and we’ll help you find a local technician we trust.

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