This article discusses the downside of swimming pool ionizers. When you’re finished, have a look at the benefits or see how pool ionizers compare with salt water pools.


Over the 20 years that pool ionizers have been on the market, staining has been the number one concern. And rightly so – if you’re going to spend tens of thousands of dollars on a pool, the last thing you want is unsightly stains.

Pool ionizers add minerals to the water to assist in controlling bacteria and algae in pools and spas by augmenting the bactericidal and algicidal activity of primary disinfectants. Like anything dissolved in the water, they can become undissolved and collect on surfaces. Left unchecked, the undissolved minerals can stain.

Why does staining happen?

Over ionization

Some swimming pool ionizer systems are not properly regulated. This could lead to ‘over ionization’ of the water where the amount of copper or other minerals put in is far higher than what is needed. For copper or copper-silver ionization to work, you only need 0.2 – 0.5ppm of copper and about one tenth of that of silver.

If the pool store says you need to increase the Total Dissolved Solids (TDS) of the water higher than 500 for the ionizer to work, that is a sure sign that it is not properly regulated, so you are better off finding a more sophisticated model.

Mineral are not chelated

Chelation (pronounced KEY-lation) is a process of bonding at the molecular level that helps to keep a compound dissolved in the water. If the minerals are not properly chelated, they tend to bond to surfaces rather than stay in the water, and this can cause staining. Modern electronic mineral systems formulate the mineral electrodes such that the minerals are properly chelated, but cheaper or older systems may not have this feature.

Water out of balance

For minerals to come out of solution, there are a few conditions that must be met. First, the mineral level has to be above 1 part per million (ppm). Second, the pH must be above 7.7 and/or the alkalinity must be above 120ppm.

It’s important to test the parameters of your pool every week or two to make sure everything is in balance. If you have a salt chlorinator, the chlorine generation process will constantly increase the pH, so it’s especially important to test on a regular basis and adjust if necessary.

Contaminated source water

The water that you fill your pool with may have a high mineral content. It is best to test your source water at a pool store before filling your pool. There may be iron, copper or manganese in the water at a high enough level to cause staining.

Contaminated salt

Salt water pools use a salt chlorinator to convert salt into liquid chlorine. They will work with most types of salt that you add to the pool. However, some salt is not properly refined so there could be contaminants mixed in that dissolve in the water and lead to staining. It’s best to buy your pool salt from a pool store to make sure it is refined properly.

Still need an oxidizer

Swimming pool ionizers allow you to reduce the chlorine and other chemicals required to maintain clean, clear water in your pool. However, the ionizer alone is not enough to do the full job. Minerals assist in controlling bacteria and algae in pools and spas by augmenting the bactericidal and algicidal activity of primary disinfectants, but they do not oxidize organic matter such as lotions, sweat and skin cells.

So, you need to use the ionizer along with an oxidizer. The most common oxidizer for pools is chlorine. Most ionizer manufacturers recommend using a reduced amount of chlorine as the oxidizer (0.5ppm to 1ppm vs 1ppm to 3ppm without an ionizer).

For smaller pools, a weekly shock treatment will also take care of the oxidizing needs.

Ozone is a natural and fast-acting oxidizer that is fed into the pool through the plumbing. Ozone is more automated than adding chlorine. However, there is an up-front cost and regulations in most countries state that you still need a low residual of chlorine, even if you have both an ionizer and ozone. Also, Ozone is short lived, does not maintain a residual and there is no way to test for it.

Can’t use stain remover / sequestering products

Pool stores will often recommend stain and scale chemicals that remove the iron, manganese and other contaminants from the water. However, with a pool ionizer, you shouldn’t use these because they also neutralize the minerals that are being added to the water. So, you will need to find another way to remove these contaminants from the water such as a pre-filter that attaches to the hose.

The exception is if your copper level rises above 1ppm. In this case, you should bring it down, and you can use a sequestering chemical for this purpose.

You have to test the water for copper

With a swimming pool ionizer, you should test the copper level every two weeks or so. This means that you need to keep a copper test kit around, or you need to visit your pool store on a regular basis. This adds one more step to your regular pool testing and maintenance.

You have to replace the cell every year or so

Swimming pool ionizers use a cell to house the minerals that are released into the water. This cell is usually composed of two rods that are either copper or a mix of copper and silver. As the minerals are released into the water, the rods wear down and typically need to be replaced every 6-12 months.

While the cost of the replacement cell is offset by the savings in chemicals, it is still an extra step that must be added to your regular maintenance.

Let us know if you can think of other problems with swimming pool ionizers. Otherwise, have a look at the benefits of pool ionizers or learn about how salt water pools and pool ionizers compare.