How to Identify and Remove Copper Stains in Your Pool (The Easy Way)

Copper stains in the pool rarely occur but are always unwelcome. But how do the copper stains get into your swimming pool, and how to get rid of them?

Copper can be introduced into your pool in several ways – from corroding metal parts to well or tap water. Copper can stain your pool walls and flooring a greenish-brown color if it’s not dealt with quickly.

Learn how to remove copper stains from your pool before they become a bigger problem.

Why is copper bad for your pool?

It’s normal for pools to have some amount of copper in them.

But if you get an overabundance of copper, like from corroded parts or old plumbing, everything goes haywire.

We want to avoid copper in our pool water. It leads to unsightly stains on the pool floor and walls. These are difficult to remove, even with an acid agent for pools.

Besides the unsightly appearance, the copper is bad for you and all other bathers.

Copper is poisonous to humans and animals. It can cause liver and nerve damage.

Therefore, it is always better to avoid copper in your pool water.

If you have a copper test kit, regularly check the copper level.

Tip: To determine if there is too much copper in your pool, simply take a water sample, add a few drops of nitric acid and shake it. The water changes color if there is copper in the pool.

What do copper stains look like in a pool?

The most distinctive effect of copper in pools is that it turns the water green under the action of sunlight.

Copper stains normally apply to a green or blue brown color in the pool.

As a result, copper-containing water is sometimes called “blue water.”

In most cases, copper stains are uniform and stretch over several meters. They are almost always isolated, but not necessarily.

The main problems occur when copper stains are visible on the pool floor or spread to the walls. This occurs very quickly and is often associated with a large amount of copper in the water.

Getting rid of these stains can be difficult because even if you drain all your water, copper stains normally reappear within a few days.

In the next chapter, I explain how copper stains in the pool happen.

How do you get copper stains in your pool?

Where does the copper come from?

As far as I know, there are five possible sources of copper in pool water: Galvanic corrosion, a high chlorine level, copper pipes, copper-based algaecides, or well water with high copper content.

  • Too much chlorine: The most common cause of copper is too much chlorine or bromine in your swimming pool. A high level of chlorine or bromine water causes an electrolysis reaction. This is where the salt in the pool corrodes iron fittings and components of other materials, releasing copper ions into the water.
  • Galvanic corrosion: A galvanic corrosion appears when you have dissimilar metals in the pool water. Sometimes, your filter pump or other equipment is made up of metal parts that are not stainless steel. If these are galvanized, you can get copper stains.
  • Copper pipes: Pipes that are made of copper can lead to stains. Especially if your pool is old, the copper pipes used in it could be corroded.
  • Algaecides: Copper-based algaecides (copper sulfate) can cause copper stains in your pool if you overdose on them. The pool water will show a brownish-green coloration. I would recommend not using these products regularly.
  • High levels of copper in the water: If there is a high level of copper in the well or tap water that your pool uses, then you can get stains as well. Even if it’s just a slight amount, the water could increase the pH level and give residuals. These stains usually show up as green stains.

How to get rid of copper stains in the swimming pool?

Removing copper from your pool is essential because it can be harmful to swimmers.

Even low levels of copper in the water may cause swimming discomforts such as itching and burning eyes, skin irritation, and excess mucus production.

Such symptoms are often mistaken for an allergy, but evidence suggests that copper exposure can activate immune responses.

Let’s see how to get rid of copper stains in the swimming pool.

  • Borax: Use Borax with a little water to form a paste. Spread it on the copper, allow it to act for several minutes, and then scrub it away with a brush. If the stains are strong, repeat this operation. Then rinse with tap water.
  • Baking soda: Bicarbonate (baking soda) is often used in combating the formation of scale in pools. It also helps to eliminate copper stains very easily. Mix baking soda with some water to form a soda paste. Then simply brush the copper stains away with a sponge.
  • Vinegar: Try to mix vinegar with water (50/50 solution) and spread the mixture on the appropriate areas with a sponge. Leave it on for about 15 minutes before scrubbing the areas.
  • Lemon juice and salt: Lemon juice is acid and could help clean the copper stains in your swimming pool. The natural cleaner is applied like vinegar to the pool and left for a few minutes. After that, the solution is wiped off with a sponge.

Some of the agents used may end up in the pool during the cleaning process.

This is not a big deal, but you should still test the water afterward and possibly balance it to avoid clouding.

Tip: In my blog article, I have described how to perform a no-drain acid wash in the pool. Just follow the link.

Prevent copper stains in your swimming pool

I always preach preventing damage than trying to fix something later.

The same goes for stains in the pool.

Here are some practical tips on how to avoid copper stains in your pool.

#1 Test the pool water chemistry

First, you must determine that the copper stains come from the pool. If you have copper plumbing at home, they could easily come from there.

Use a special copper water tester or test strips to determine the levels of copper in the pool.

This will help you remove the cause and solve this problem faster.

If it is indeed your pool that causes the stains, try to determine whether they are caused by too much chlorine or high levels of algaecides.

You should also test the pH level because a low pH level (below 7.0) makes the water acidic and may result in copper stains.

#2 Clean the filter

If the filtration system is not working properly, it will not remove copper from the water.

When you can see copper stains in the skimmer box, this could mean that the filter system is clogged or dirty.

You need to clean it immediately if it seems to be causing the problem.

Tip: Backwashing your pool filter followed by rinsing should be performed every 10 to 14 days. In my blog, I explain to you exactly how this works.

#3 Use a pool flocculant

Flocculants are a gentle way to reduce copper levels in pool water.

Place a Flocculation pad in your skimmer and let it do its work.

It can tackle both copper and iron, as well as a host of other metals that might be present in your pool water.

The flocculant will stay active for up to 10 days after being placed in the skimmer basket, so you have plenty of time to use it.

You should know that this does not mean that the flocculant will remove copper from your pool by itself or reduce your daily maintenance. In fact, this is a supplement to the filter and pool cleaning chemicals you use in your swimming pool.

#4 Don’t use copper-based algaecide

Most algaecides have copper as one of the ingredients.

So if you use those products, there is a bigger risk that you will end up with copper stains on your pool surface.

The algaecide could cause pool foam or green hair in the worst case.

So try to use algaecides as little as possible.

Before using a copper-based algaecide, read the label and follow all of its directions.

Most importantly, remove as much loose dirt and debris from your pool surface before dosing with any type of algaecide.

#5 Don’t over chlorinate your swimming pool

Like I already said, chlorine can oxidize metal ions in the pool water.

So if there is too much chlorine, it starts working on copper ions and turns them into green spots on your walls and floor.

If this happens, back off the amount of bleach you add and try to lower the level if it is too high.

Tip: Read my post about lowering the chlorine level in your swimming pool.

 #6 Change the location of the chlorinator

The location of your chlorinator or salt system in relation to your pool heater is one of the more surprising reasons you can get copper staining.

These items should always come after the heater to save it from constantly being hit with freshly chlorinated water.

How to repair copper stains coming through plaster on inground pools?

Let’s say you have a pool that is stained from copper. They are mostly black but can also be red, green, or brownish.

The stains often occur on the floor steps of the pool and on the walls. The metal makes your water look bad and can also cause serious damage to your plaster – although this may not be visible immediately.

The damage is done on the outside of your pool, but it can also cause corrosion to metal parts on the inside of your pool.

If this goes unnoticed, you will have to replace the liner or foot valves. And if you have small children in your family or friends who visit often, you do not want them near a pool with hazardous chemicals.

You can, however, restore your pool to its full beauty again – by removing the stains. But you must act quickly once you have spotted them!

To repair copper stains coming through plaster on in-ground pools, you have to:

  1. Use a brush to remove the stains. This is usually sufficient for small areas.
  2. You can also use an acid such as vinegar or muriatic acid, which should only be mixed in water and not be applied directly to the pool.

For greater damage, you may have to resurface your pool.

This is a less expensive option than replacing the plaster. Sometimes, you can use this technique to remove old plaster and apply new, if it’s still in good condition.

Is it safe to swim in a pool with copper?

Small amounts of copper are beneficial to chlorination because chlorine is more active with copper.

If the number of copper increases, it becomes toxic for you.

Then there are green or dark brown stains on the pool floor and walls caused by copper oxide scale – also called cupric sulfate scale.

On the other hand, large amounts of copper can cause serious health problems for humans and animals.

As long as your pool water looks clean and is filtered daily for 6 to 8 hours, you don’t have to worry.

At the latest, if you notice copper stains in the pool or the water turns dark, I would recommend that you take care of the problem before swimming in the pool again.

Do you have further questions about copper stains in your pool?

The best way to contact me is @contactswimfool on Twitter or Pinterest. I am happy to help you.

Have fun swimming!

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Hi. I'm Max Berg. I've been in the pool industry since 2015 and have always felt drawn to water. I'm the author behind swimfool.com, where I share my years of experience in pool maintenance and give helpful tips on keeping a swimming pool or hot tub clean. My tips reduce the costs of water treatment and protect the environment.

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