Pool Filter Cartridge Blue: 3 Reasons and 2 Helpful Solutions

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Why Is My Pool Filter Cartridge Blue?

Did you notice a blue powdery deposit on the cartridge pleats, while cleaning them? It is not normal but it can happen. So, why is your pool filter cartridge blue?

Powdery blue deposit on the pleats of the pool filter cartridge is most likely a salt of copper such as copper sulfate or copper chloride. Most copper salts are blue, green or somewhere in between.

Copper has no place in your swimming pool. Unfortunately there are many ways in which copper can get into your pool. Here is how:

How Does Copper Get into My Pool?

1. Ground Water

All water from natural sources has a range of minerals, including copper dissolved in it. Areas with mining, farming, manufacturing tend to have higher levels.

Municipal tap water is treated to keep the copper level within EPA guidelines. But some water sources, such as ground or well water, have a high content of copper.

Ground water tends to be rich in minerals that it picks up from rocks & earth. So if you use well water to fill up or replenish your pool, you are adding copper to your pool too.

2. Pool Heaters

Copper pipes in pool heaters and solar equipment can corrode. The chances increase if the pH level of the pool remains low (acidic) over prolonged periods. Copper can then find its way into your pool.

3. Pool Chemicals

Algaecides can be a source of copper for your pool. Many algaecides are copper based and use copper sulfate or copper chelates as the key ingredient.

Kem-Tek Pool & Spa Concentrated Algaecide is very effective for prevention of algae and also helps to clarify cloudy pool water. Best of all it is copper free!

Keeping your pool chlorine free comes with a cost. Many chlorine alternatives to chlorination will end up adding copper to the pool water. These include mineral systems, ionizers and “natural” sanitizers & shocks.

Low quality pool salts may also contain copper.

The trouble with copper in your pool is that it stays there and keeps building up. Copper can make your pool appear cloudy blue. Copper salts will make your pool filter cartridge blue. Worse, they will stain your pool and turn blonde hair & fingernails green.

How Do You Remove Copper from a Pool?

The first thing to do is, of course, to test the pool water and find out the exact copper level in the pool. You can do this by using test strips or taking a sample of your pool water to the local pool chemical supplies dealer.

Ideally the copper level should be zero, but that is highly unlikely. If the copper level in your pool is below 0.4 ppm you are OK. No need to worry too much!

In case the copper level is higher than 0.4 ppm, you need to consider the various options for reducing the copper level. Some of the options are:

1. Diluting your Pool Water

In theory it is pretty simple. Let us say the copper level in your pool is 0.6 ppm. Drain out half the water in your pool and replace it with water that has 0 ppm of copper. You will end up with a pool with a copper level of 0.3 ppm.

Easier said than done though! You can not drain out half your inground pool in one go. Your pool will “pop” due to hydrostatic pressure from the surrounding earth. So you will need to conduct the entire exercise in small steps.

More importantly, draining pool water means you are losing precious pool chemicals along with it too.

My advice is to ensure that the water that you use to replenish your pool is copper free. 

Use this source whenever you have to compensate for water lost due to evaporation or vacuuming to waste. Gradually the copper level will come down to below 0.4 ppm.

2. Use Sequestering Agents

First things first. Sequestering Agents will not remove copper stains from your pool. They will not even remove copper from your pool.

Sequestering Agents are chemicals that bind up the copper in a chemical bond. In other words they “lock up” the copper. The copper stays in the pool but does no harm as it is not active. So it prevents a pool with high copper content from going cloudy or getting stained.

Check out Jack’s Magic The Blue Stuff on Amazon. It really works!

Thank you very much for reading the post. I do hope you found it informative and helpful.