🟡 Why does my fiberglass pool have yellow stains?

1. Presence of metals in the water (iron or copper)

Yellow or brownish stains are often due to the oxidation of metals present in the water, such as:

-Iron (often present in well water)

-Copper (from pipes or chlorine treatment containing copper-based algaecides)

➡️ What happens: When you add chlorine, these metals can oxidize and deposit on the pool surface , leaving stubborn stains.

2. Mustard seaweed

Sometimes a yellow stain can be caused by yellow algae (mustard algae) , which easily clings to pool walls, especially in shaded areas.

➡️ Features:

- Mustard yellow color

-Powdery texture

-Often resistant to chlorine

3. Improperly balanced chemicals

An imbalance in pH, alkalinity, or stabilizer can promote staining, especially if metals are present in the water.
We recommend keeping the pH slightly lower than the norm between 6.8-7.2

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🧽 How to remove yellow stains from a fiberglass pool?

If it is metal:

Have the water tested for the presence of metals (at a specialist store such as Piscines Geyser)

Use a metal sequestrant to neutralize them

Avoid shocking water with chlorine without first neutralizing the metals

If it is mustard algae:

Brush off stains with a soft brush

Increase the chlorine level (shock treatment)

Add a specific algaecide for mustard algae

Let the filtration run for 24 to 48 hours

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🔄 Prevention of yellow spots

Regular water analysis (pH, chlorine, metals)

Avoid iron-rich water sources (such as wells)

Add a metal sequestrant when opening the pool

Maintain good circulation and clean lightly circulated areas

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🛠️ Need help?

📍 Come to Piscines Geyser with a water sample for a free analysis.
We will recommend the right products to identify and permanently remove yellow stains from your fiber pool.