Liner stains: where they come from and how to remove them
Most liner stains come from metals in the water, from leaves, or from sunscreen at the waterline. Their colour usually points to the cause, and the cause points to the cleaning method.
Identify the stain by its colour
| Stain colour | Likely cause | What to do |
|---|---|---|
| Brown, reddish, rust-like | Iron from a borehole, or a rusty object in the water | Metal stain remover plus a metal sequestrant |
| Blue-green | Copper, from ionization or from copper parts combined with low pH | Correct the pH, add a metal sequestrant, find the source |
| Purple or black | Manganese, usually from a borehole | As for iron |
| Yellow-brown, leaf-shaped | Tannins from leaves, fruit, pits | Remove, brush, keep chlorine correct |
| Yellowish or grey band at water level | Sunscreen, body oils, dust | Waterline cleaner suitable for PVC |
| White, dull, rough | Calcium scale | Adjust the hardness and use a mild scale remover |
| Bleached, lighter patch | Chlorine granules that settled on the liner | Cannot be cleaned; prevention only |
Metal stains
Metals are dissolved in the water and deposit on the liner when the chemistry changes, usually after shock chlorination or a sudden rise in pH. That is why they often appear suddenly, over a large part of the floor rather than in one spot.
A simple test tells a metal stain from an organic one: hold a vitamin C tablet against the stain for a little while. If it fades, it is probably metal; if not, it is most likely organic. Metal stains are treated with special products, often based on ascorbic acid, followed by a metal sequestrant so they don't settle again. After a treatment like this, check pH and chlorine again.
Prevention is easier than cure. If you fill from a borehole, have the water analysed before the first fill. If you are considering a copper-silver system, first read what to watch out for with pool ionization, especially with a light-coloured liner.
Organic stains and the waterline
Leaves, pine needles, pits and fruit leave brown imprints when they sit on the floor for days. They usually come off with brushing and the right chlorine level, as long as they are not old. The best prevention is simple: skim with the leaf net before they sink, and cover the pool when it is windy.
The waterline collects everything that floats: sunscreen, body oils, pollen and dust. A yellowish or grey band forms, more visible on light-coloured liners. Clean it with a soft sponge and a cleaner made for PVC waterlines, before it has a chance to harden. A shower before the pool noticeably reduces the problem, because most of the oils are rinsed off before they reach the water.
What never to do to a liner
- Don't use steel wool, hard brushes, scouring powders or solvents.
- Don't throw granular chlorine directly onto the liner; dissolve it first in a bucket of water, as described in pool chlorine.
- Don't pour concentrated acid or scale remover directly onto one spot.
- Don't mix products together.
- Don't drain the pool to scrub the floor: a liner pool is never fully drained.
Bleached chlorine marks and very old metal stains may never come out completely. If the liner is covered in marks like these and the look bothers you, the solution is a liner replacement.
Questions
Why did stains appear right after shock chlorination?
Strong chlorine oxidizes dissolved metals and makes them settle on the liner surface. If your water contains iron or copper, add a metal sequestrant before the shock.
Which liner colour shows stains the least?
Mid tones such as sand and light grey, as well as mosaic, hide small marks best. White shows dark stains and anthracite shows scale; see liner colours.
See also
Pool chlorine
Pool chlorine as tablets, granules or liquid: which form suits you, what free and combined chlorine are, and…
Water hardness
Pool water hardness: what calcium does, why scale forms at the waterline, what to expect on islands and with…
Liner colours
Pool liner colours: how white, light blue, grey, sand and green change the look of the water, its temperature…