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Yellow, brown or grey stains, yellowed waterline, liner losing its colour: these problems almost always have the same origin, the water. Some stains can be removed, others cannot. That is why it pays to know the causes so you can avoid them.
- Yellow, brown, grey stains: most often metals (copper, iron, manganese).
- Yellow waterline: often copper reacting with sun creams.
- Liner losing its colour: too much chlorine, low pH, water too warm.
- Prevention: metal sequestrant when filling, mains water, no copper-based products.
Identifying the stain
| What you see | Likely cause | What to do |
|---|---|---|
| Yellow, brown or rust-coloured stains, often on the floor | Iron or manganese (borehole water, well water, water of unknown origin) | Metal sequestrant; stop using this water; try a metal stain remover |
| Yellow waterline, yellowish stains | Copper (copper-based algaecide or tablet) + sun creams | Stop the copper-based product, metal sequestrant |
| Grey or blackish stains | Metal sulphides (metals coming out of solution) | Metal sequestrant; ask for advice, often irreversible |
| Liner losing its colour, washed-out look | Too much chlorine, low pH, warm water | Get back to the right values; fading cannot be reversed |
| Faded patch in one spot | Chemical left against the liner (tablet, granules, stuck dispenser) | Always dose through the skimmer; the faded patch is permanent |
| Rough white deposit on the waterline | Limescale (high TH) | Suitable waterline cleaner + limescale sequestrant |
Copper: the liner's enemy
Above 0.1 mg/L, copper causes yellow stains, a yellow waterline and metal sulphide stains. It gets into the water in two main ways:
- treatment products that contain it: some algaecides (especially “shock” algaecides for resistant algae) and some multifunction tablets containing copper sulphate;
- fill water loaded with metals (borehole, well, spring).
Read the composition of your products, especially algaecides and multi-action chlorine. With a liner, choose algaecides that are copper-free, preferably based on quaternary ammonium.
Fill water
Fill and top up with mains water (tap water). Borehole water or water of unknown origin must be chemically treated first to remove dissolved iron, copper or manganese. Otherwise these metals settle on the membrane and stain it.
If stains are already there
- Find the cause first: have the water tested (copper, iron) and check the composition of your products. Otherwise the stains will come back.
- Add a metal sequestrant to stop new deposits.
- For recent metal stains, a metal stain remover can help. Follow the instructions exactly (adjusting the pH before treatment, etc.).
- Fading (washed-out liner) cannot be reversed: you can only stop it getting worse.
Products against metal stains
A copper-free algaecide
Frequently asked questions
Why does my liner have yellow stains?
Most often because of copper or iron dissolved in the water. Copper comes from some treatment products or from metal-laden fill water; it also reacts with sun creams and turns the waterline yellow.
Do stains on a liner come off?
Recent metal stains can sometimes be reduced with a metal stain remover. Fading and old stains are generally irreversible.
Can I fill a liner pool with borehole water?
Liner manufacturers advise against it. If you have no other choice, the water must be treated for metals first, and a metal sequestrant is essential.
How do I know if a product contains copper?
Read the composition on the label or the product sheet. Be especially careful with algaecides for resistant algae and multifunction tablets.
What is the maximum copper level in a liner pool?
0.1 mg/L. Above that, permanent stains can appear.