Copper-silver ionization in the pool: what you gain and what to watch

How copper-silver ionization works

The unit is fitted into the plant room circuit, usually after the filter. Inside a chamber there are electrodes made of a copper-silver alloy. A controller passes a weak current through them and the electrodes slowly release ions into the circulating water.

• Copper acts mainly against algae.
• Silver acts against bacteria, but much more slowly than chlorine.
• The amount of ions is set by the controller and checked with a copper test kit.

Ions do not evaporate and are not destroyed by sunlight the way chlorine is, so they stay in the water for a long time. That is the advantage of the method, but also the cause of most problems when the concentration gets out of hand.

Why it does not replace chlorine

Ionization disinfects slowly and does not oxidize. In other words, it does not “burn off” sweat, sunscreen and the other organic matter that swimmers bring in, nor does it quickly neutralize a germ that has just entered the water. That is why the pool always needs a residual disinfectant as well.

In practice, ionization lets you keep free chlorine towards the lower end of the 1–3 mg/l range and use less algaecide. It does not let you drop it to zero. The same goes for other supplementary technologies, such as UV disinfection: they reduce the need for chlorine, they do not replace it.

The risk of stains on a light-coloured liner

Copper stays dissolved as long as the water is balanced. When the pH rises, when alkalinity is high or when you add a large dose of oxidizer for shock chlorination, some of the copper comes out of solution. The result is blue-green, brownish or greyish stains on the liner, usually on the floor and around the return inlets. On a white, light blue or light grey liner they show up strongly and do not always come off with ordinary cleaning.

The same copper can give blonde hair a greenish tint. If the fill water comes from a borehole that contains metals, the risk is higher, because the metals add up.

If you choose it: rules for use

1. Keep the pH steady at 7.2–7.6. This is the most important protection against stains.
2. Test copper regularly, along with chlorine and pH, and keep it very low, as the unit's manufacturer specifies.
3. Start with a low ion setting and raise it only if needed. Do not add extra “just to be safe”.
4. Before shock chlorination, check pH and copper. If copper is high, ask about a metal sequestrant.
5. Clean scale off the electrodes and replace them when they wear out.
6. When the pool is closed for winter, the unit is usually switched off or runs at the minimum.

If you see the first signs of discolouration, stop the unit and test the water before you do anything else. What to do next is covered in the article on stains on the liner.

Who it makes sense for

Ionization suits an owner who tests the water systematically, has moderate use and wants less chlorine and fewer algaecides. In a holiday rental pool with many bathers, the need for fast oxidation stays high, so the benefit shrinks. If what you mainly want is a gentler feel to the water, also compare salt chlorination. We discuss which system suits your pool at the site survey.

Questions

See also