How to Remove Stains from Your Pool

By November 17, 2020Pool Safety

Written by Barack James and published on

Stains on your pool can be embarrassing and can make enjoying your pool with friends and family difficult. Some pool stains are hard to remove and may require more than just brushing to remove them.

In some cases, you may need to use powerful chemicals and other pool cleaning methods to treat your pool stains and prevent future stains from forming.

How to Remove and Prevent Metal Stains in a Swimming Pool

Fixing a Swimming Pool’s Metal Stains

Swimming pools with water sourced from a well are prone to developing stains due to the presence of heavy metal compounds like iron, copper, silver, and manganese.

Oxidised iron turns pool parts and water to a brown or rusty colour, copper turns pool parts and water to light green, silver turns pool parts and water to black, and manganese turns pool parts and water to purple.

Metal stains occur mainly when chlorine is added in water, oxidising these heavy metals to produce different stain colours, depending on the metals present in your water. These stains might occur at different places inside and around your pool, including:

  • in the pool water,
  • along the bottom or walls of the pool,
  • along a vinyl liner or on fibreglass surfaces, and
  • across the steps or on various pieces of pool equipment.

In this article, we will break down how to:

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

Step 1: Testing the Pool Water—Is It Metal Staining or Algae?

Before taking any action to undergo treatment for metal stains, you need to be certain it’s metal staining. Green or black stains might indicate metal stains, but they may also occur as a result of green or black algae. Do the vitamin C test by using ascorbic acid to determine whether it’s metal staining or not:

  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.
Metal Stains Before and After Removal

Metal Stains Before and After Removal


Step 2: Getting Rid of Metal Stains in 5 Easy Steps

Here is an easy five-step breakdown of how to remove metal stains from your pool.

1. Lower the Free Chlorine Level to 0.0 ppm

Before adding ascorbic acid, ensure that you take down the chlorine level to 0.0 ppm using a neutralizing chemical, direct sunlight, or by partially draining and refilling your pool with fresh water. Lowering chlorine to 0.0 ppm is necessary, as chlorine will cause more stains, and you may need more ascorbic acid to clear the stains.

Important Note: Since clearing all metal stains may take a couple of days with zero free chlorine, you can use ProTeam Polyquat 60 Algaecide. I recommend this because it has no copper compounds that may worsen the stains, has no ammonia that can cause extremely cloudy water that is not easy to clear, and can be effective in fighting and preventing any type of algae that might thrive in your water.

2. Lower the pH Level to 7.2

Lower your pH level to 7.2 using muriatic acid if it’s higher than that. This is necessary since high pH levels may need a lot of ascorbic acid to be able to clear metal stains and may also contribute to more metal staining, and that is what you need to get rid of. I prefer muriatic acid, since pH minus will not lower the total alkalinity (TA)—and high TA might cause pH to scale high if the process of clearing stains take longer.

  1. Put your pool’s filter on circulation.
  2. You need about 1 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 around the perimeter, targeting most stain-affected areas.
  4. Let the ascorbic acid circulate for around 30 minutes, and watch the metal stains fade away slowly before your eyes. If you still see small stains after 30 minutes, add more ascorbic acid on those spots while the filter is on for at least 24 hours.
  5. After 24 hours, all the stains should have faded away. Start re-balancing your water chemistry after 24 hours.

4. Get pH and Alkalinity Back to Normal Levels

Ascorbic acid is strong and will definitely bring down pH and TA levels. If the pH and TA are not way out of balance, you can use 20 Mule Team Borax to raise the pH without affecting TA and an alkalinity increaser to bring the TA up to recommended levels when it gets low. Add these chemicals slowly while testing until they get to recommended levels, since you don’t want pH or TA to get out of balance.

Remember that pH should be maintained between 7.4 and 7.6 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 chemical readings. If by mistake you get your pH and TA out of balance and they get troublesome to balance, here is more about how you can balance pH and TA.

5. Get Chlorine Back to Normal Levels

Raise your free chlorine level to 1.0 or 2.0 and leave it there. 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 a chlorine/cyanuric acid chart or pool calculator to find the accurate amount of free chlorine you need.

After getting chlorine to the recommended level between 1 and 2 ppm, 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 Note: High levels of pH and chlorine will definitely precipitate any metal compound in your water if not treated (sequestered) or removed out of your water.

Step 3: 3 Ways to Prevent Metal Staining in the Future

Here is a breakdown of three simple ways to prevent metal stains from building up in the future.

1. Remove Metal Compounds From Your Fill-Water

Some years back, before CuLator metal eliminator was available, there was no practical way of removing metallic compounds from pool fill-water before entering your pool. The only possible way was to treat water inside your pool, which is hard work and expensive to maintain.

CuLator Ultra Power Park is now my best option for this, because you can use it in the skimmer or pump basket to remove up to 4 ppm metal compounds from 20,000 gallons of fill-water before entering your pool. If your pool is more than 20,000 gallons, you can increase your parks and use them both in the skimmer and pump basket.

CuLator should work up to 30 days or longer depending on the level of metal in your water and is replaceable once worn out.

Moreover, you need to be careful with the chemicals you add in your pool, since copper may find its way in your pool from chemicals such as algaecide or ionizer—and from eroded pool parts with copper. If you can’t use CuLator for any reason, detailed below are more ways to control metal stains in your pool.

2. Add Metal Remover in Your Pool Water

Metal remover is one of my best options, because it works by removing heavy metals in your pool water through the filter, leaving your water clean and free of heavy metals that cause stains when chlorine is added or pH levels scale high. Metal Magic by Pro Team is my preferred option, since it removes all common metals from your water, including copper, iron, silver, and manganese.

Metal Magic is non-foaming, pH neutral, and won’t affect your pH levels or cause foaming inside and around your pool. Moreover, it also removes current metal stains from your pool and scales from surfaces. It crystallizes and removes metals from pool water through the pool filter. Metal Magic is compatible with all types of filtration systems, and it doesn’t matter which filter your pool runs on. This product also protects plumbing and equipment, which is an added advantage on your pool parts.

If you decide to use Metal Magic, the product dosage for initial treatment is 32 fluid ounces per 10,000 gallons of water. That is, if you have a 20,000-gallon pool, you will add 64 fluid ounces to be able to remove all metal compounds in your pool water.

The easiest way to avoid stains in your pool, however, is to avoid fill-water with metals. Before installing your pool, it is important to test your water source for metal content and avoid water sources with metals in it at all costs, because maintenance will be relatively hard and expensive in the long run.

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