How to Remove and Prevent Metal Stains in a Swimming Pool

Updated on October 23, 2017
Barack James profile image

Barack is a chemical engineer with a knack for pool chemistry. He has been in the pool maintenance industry for 8 years.

Brown Metal Stains on Pool Stairs and Metal
Brown Metal Stains on Pool Stairs and Metal | Source

Fixing a Swimming Pool's Metal Stains

Swimming pools with water sourced from a well are prone to developing stains due to metal compounds (like iron and copper) present in well water. Rusty, dark stains occur when pH and chlorine are out of balance.

This article including the video at the end explain how to:

  1. test the water,
  2. get rid of metal stains in 5 steps, and
  3. prevent staining in the future.

Metal stains are very common with water that has lots of metal components in it. The stains might look black, green, rusty brown, orange, or yellow, and you might find them on...

  • the bottom or walls of the pool,
  • along a vinyl liner or on fiberglass surfaces, or
  • on the steps or on various pieces of pool equipment.

Step One: Test the Pool Water: Is it Metal Stains or Algae?

Before taking any action to treat for stains, you need to be certain of the cause. Green, yellow, or black stains might indicate metal stains, but may also occur as a result of algae.

Try the vitamin C test and use ascorbic acid to determine what kind of stain it is:

  1. Hold a vitamin C tablet against a potion of the stain for about 30 seconds.
  2. If the stain vanishes or lightens, then it is metal stain and not algae.

Step Two: Get Rid of Metal Stains in 5 Easy Steps

1: Lower Chlorine Level to 0.0 ppm

Before adding ascorbic acid, ensure that you take down chlorine level to 0.0 ppm using a neutralizing chemical, direct sunlight, or diluting using fresh water.

Lowering chlorine to 0 ppm is necessary, as chlorine will immediately eat up ascorbic acid.

Very important; you can use poyquat 60 as directed during this process to prevent algae from thriving in the water while your chlorine is at 0 ppm.

2: Lower pH Level to 7.2

Lower your pH level to 7.2 if it’s higher than that: This is necessary since high pH levels cause metal staining and that is what you need to get rid of.

3: Run Filter and Add Ascorbic Acid

  1. Put your pool's filter on circulation.
  2. You need about one pound of ascorbic acid for every 10,000 gallons, so the amount to add will depend on the volume of your pool.
  3. Using a tin or a cup, drop the ascorbic acid down the sides of the pool all round the perimeter.
  4. Let the ascorbic acid circulate for around 30 minutes and watch the metal stains fade away before your eyes. If you still see small stains after 30 minutes, add more ascorbic acid on those spots while the filter is on.
  5. Leave the filter on 24/7.
  6. After 24 hours, all the stains should have faded away.
  7. Start re-balancing your water chemistry after 24 hours.

4: Get pH and Alkalinity Back to Normal Levels

Ascorbic is strong and will definitely bring down pH and total alkalinity (TA) levels. You can use soda ash (washing soda) to bring up pH and TA to recommended levels slowly, while testing, since you don’t want pH or TA to get out of balance again.

Remember that pH should be maintained around 7.2 to avoid metal staining: I prefer using LaMotte ColorQ Pro 7 digital pool water test kit since it is very accurate and fast in taking all chemicals readings.

If your TA is within the recommended level but you still need to raise your pH, you can use borax, which may have small effect on TA, but not like soda ash.

5: Get Chlorine Back to Normal Levels

Raise your free chlorine level to 1.0 or 2.0 and leave it there for two weeks. You need to use liquid chlorine bleach for this purpose.

Be cautious while adding chlorine and watch for any staining in the process. Ensure that you keep your chlorine at the minimum level possible depending on the available cyanuric acid level.

You can use chlorine/Cyanuric acid chart or pool calculator to find the accurate amount of free chlorine you need.

After getting chlorine to recommended level, avoid shocking your pool for about two weeks to allow the ascorbic acid to be completely used up. After about two weeks, you will notice chlorine being used up as usual. You can then begin to shock your pool carefully to avoid adding excess chlorine.

Important: High levels of pH and chlorine will definitely precipitate any metal compound that is not treated (sequestered).

Metal Stains Before and After Removal
Metal Stains Before and After Removal | Source

Step Three: How to Prevent Metal Staining

Prevent metal stains from forming by treating the pool water using a sequestrant.

Ideally, regular doses of sequestrants will prevent metal staining when pH or free chlorine is added into the water.

Sequestrants naturally bind to the metal, preventing them from depositing stains.

The most effective sequestrants are derived from phosphonic acid. I recommend Metal Magic by Pro Team since it is very effective. Alternative brands are:

1. Natural Chemistry Stain-Free
2. The Magenta Stuff by Jack's Magic

Sequestrants slowly break down in the water so you need to add it regularly to maintain correct levels.

Finally, using borates may be useful since borate ensures more stable pH by preventing pH from drifting and reducing chlorine usage, since it act as a sanitizer.

Good luck and happy swimming!

How to Remove Metal Compounds from Pool Water

Some years back, before CuLator metal eliminator was available, there was no practical way of removing metallic compounds from pool water, and the only possible way was to completely drain the pool and then refill it with fresh water. Lots of work, right?

Now, you can use CuLator in the skimmer or pump basket, which should work up to 30 days or longer depending on the level of metal in your water.

Before installing a pool, it is important to test your water source for metal content and avoid water sources with metals in it at all cost maintenance will be relatively hard and expensive.

Metals that may cause staining are copper, manganese, cobalt, nickel, and silver. However, copper may find its way in from chemicals used such as algaecide or ionizer, and from eroded pool parts with copper.

What If the Water Is Cloudy?

If metal staining is the only problem, the pool water should remain clear and not cloudy. In most cases, murky or cloudy pool water is not associated with metal stains.

© 2015 Barack James


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    • Barack James profile image

      Barack James 2 years ago from Green City in the Sun

      Thumbi7: Thanks alot for your comment, that's so encouraging. Thanks for sharing too, it will definitely help someone.

    • thumbi7 profile image

      JR Krishna 2 years ago from India

      Very informative hub. Interesting read

      Voted up and shared