Stains on Pool Liner: Brown, Yellow, Green, or Black Patches

Quick answer: Stains can be organic, metallic, or biological. Identify the type first, then choose the right chemical treatment.

This topic comes from recurring questions pool and hot tub owners ask: what to measure first, what to dose, when to filter, and when it’s no longer worth trying to save the water blindly.

Common causes

• Metals in the water.
• Leaves and organic debris.
• Algae in the surface pores.
• Localized scale deposits.
• Unsuitable brushes or chemicals.

Step-by-step procedure

1. Photograph and observe the color of the stain.
2. Test the pH and disinfection level.
3. Try mechanical cleaning with a suitable brush.
4. Use a metal treatment product for metallic stains.
5. Address disinfection and filtration for organic stains.

What to avoid

• Don’t dose chemicals without measuring.
• Don’t mix different disinfection systems without knowing the instructions.
• Don’t wait for a small problem to turn into major cloudiness.

How to prevent it next time

• Measure the water regularly and keep a log of your actions.
• Keep the filtration system and filters clean.
• React immediately after heavy bather load.
• Follow the manufacturer’s instructions for the pool, hot tub, and chemicals.

When to call a service technician or expert

Call a service technician or expert if the problem keeps recurring, the water smells, bathers experience discomfort after swimming, or you’re unsure about the technology and dosing.

Frequently asked questions

Should I adjust the pH first, or add disinfectant first?

In most common situations, measure and correct the pH first, because disinfection performs worse outside the correct range.

Is a generic tip from the internet enough?

Not always. Water volume, filtration type, water source, and the chemicals used all matter. Treat an online guide as a checklist, not a substitute for measuring.

Sources and editorial note

• ALBIXON – most common pool water problems
• ARIVA – green water in the pool
• Upravvodu.cz – pool water problems
• ALBIXON – hot tub water care
• Laboratoř Monitoring – hot tub water treatment
• AquaFinesse – guide to hot tub water care
• CDC – home pools and hot tubs, water testing
• CDC – hot tub safety
• Modrá střecha – pool discussion forum
• eMimino – pool and hot tub experiences
• Reddit r/hottub – common water problems
• Trouble Free Pool – pool water problem forum

This article is an editorial guide for home pools and hot tubs. Always follow the technology manufacturer’s instructions and the chemical safety data sheets. Stricter hygiene rules apply to public facilities.