How to Remove and Prevent Metal Stains in a Swimming Pool

Updated on May 25, 2019
Barack James profile image

Barack is an expert pool chemistry guy and experienced online-based pool maintenance assistant via in-depth articles that top search results

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 heavy metal compounds like Iron, Copper, Silver, and Manganese presence.

Metal stains occur mainly when chlorine is added in water, oxidising these heavy metals to produce different stain colours depending on the metal present in your water.

Iron is oxidised turning pool parts and water to brown or rusty colour, Copper is oxidised turning pool parts and water to light green, Silver is oxidised turning pool parts and water to black, and Manganese is oxidised turning pool parts and water to purple. This article explains how to:

  1. Test the water for metal stains
  2. Get rid of metal stains in 5 steps, and
  3. How to prevent staining in the future.

Metal stains might occur at different places inside and around your pool including:-

  • Pool water
  • The bottom or walls of the pool
  • Along a vinyl liner or on fibreglass surfaces
  • 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 undergo treatment for metal stains, you need to be certain it's metal stain because green or black stains might indicate metal stains, but 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 stain 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.

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

1: Lower Free 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 partially drain and refill 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.

Very important; since clearing all metal stains may take a couple of days with zero Free Chlorine, you can use ProTeam Polyquat 60 Algaecide, which I recommend because has no Copper compounds that may worsen the stains, and ammonia that will cause extremely cloudy water that is not easy to clear, and not forgetting effectiveness in fighting and preventing any type of algae that might thrive in your water.

2: Lower 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 TA and high TA might cause pH to scale high if the process of clearing stains take longer.

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 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 total alkalinity (TA) levels. If the pH and TA are not way out of balance, you can use 20 Mule Team Borate to raise the pH without affecting TA, and Alkalinity increaser to bring TA level up to recommended level when low. Add these chemicals slowly while testing till they get to recommended 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 chemicals 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 chlorine/Cyanuric acid chart or pool calculator to find the accurate amount of free chlorine you need.

After getting chlorine to recommended level between 1 and 2ppm, 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 in your water if not treated (sequestered), or metals removed out of your water.

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

Step Three: 3 Ways to Prevent Metal Staining 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, and the only possible way was to treat water inside your pool, which is hard work and expensive to maintain.

CuLator Ultra Power Park is my best option because you can use it in the skimmer or pump basket to remove upto 4ppm metal componds from 20,000 gallons fill-water before entering your pool. If your pool is more than 20k 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.

The only easiest way to avoid stains in your pool 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 cost because maintenance will be relatively hard and expensive in the long run.

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 reasons, below are more ways to control metal stains in your pool.

2. Add Metal Remover in Your Pool Water

Metal remover is my best option 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 the option since it removes all common metals from your water including Copper, Iron, Silver, and Manganese.

Metal Magic is non-foaming and pH neutral and won't affect your pH levels or cause foaming inside and around your pool. Moreover, Metal Magic removes metal stains from your pool and scales from surfaces if already affected.

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, such that if you have a 20,000 gallons pool, you will add 62 fluid ounces to be able to remove all metal compounds in your pool water.

After the initial treatment dose, you will need to add this metal remover after a given period to keep your water free of metals. The routine maintenance dose should be between 3-6 fluid ounces per 10,000 gallons of water per month.

The second option I highly recommend for pool owners is Orenda SC-100. Orenda SC-100 is one of the most effective calcium and metal stain reducer on the market and I prefer it when fighting high calcium levels, calcium build-up, and scales, both in harsh chlorine based pool and saltwater pool.

This product is nontoxic and nonhazardous to your pool since it contains no phosphorus, which is a major contributor to algae growth in swimming pools. Like Metal Magic, Orendas SC-100 prevents and removes calcium scale from pool surfaces and prevents metals from staining pool surfaces when chlorine in added.

Moreover, this product improves life and functionality of Salt Chlorine Generators by preventing scaling, which extends salt cell life and also stops calcium buildup before it starts, and I recommend Orendas SC-100 specifically for saltwater pools that has metals, scales, and calcium build-up.

For better result, Orendas SC-100 should be added in initial dose, and frequent doses to to keep heavy metals from your water.

For initial dose: 1 quart per 10,000 gallons when pool is full should be added. For maintenance dose: 6 ounces per 10,000 gallons every other week is enough to get rid of all metals in your water and prevent metal staining when chlorine is added or pH scales high for any reason.

3. Add Metal Sequestrant in Your Pool Water

Metal sequestrant should be the last option to use in pool because it works differently from metal removers like Metal Magic and Orendas SC-100: Metal sequestrant does not remove metals in your pool water, but it naturally binds into the metals, holding metal particles together in your water so that they don't come out of the solution to react with chlorine when added in your water or when pH levels get too high.

Ideally, regular doses of sequestrants will prevent metal staining when chlorine is added into the water and slowly break down, and therefore should be introduced regularly in your pool water to maintain the right level to keep stains away from your pool.

The most effective sequestrants are derived from phosphonic acid, and the best in the market today is Pool Mate Metal Out. This product helps prevent discoloration of pool water with Iron, Silver, Manganese, Copper and other metals and minerals which may be present in the water supply.

Pool Mate Metal Out is an excellent general purpose sequestrant which helps protect plumbing and pool walls from rust, stain and scale. It should be used for pool openings and closings and throughout the season for best results, add 1 quart per 10,000 gallons on a weekly basis and you will never have metal stains in your pool.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

  • I tried the vitamin C test with my swimming pool and it turned the stain brown. What should I do next?

    The brown stain means you have Iron in your pool water. To get rid of the stains, follow these steps:

    1. Get your free chlorine to 0.0ppm by not adding more chlorine, this might take a few hours or days depending on the level of FC in your water.

    2. Add polyquat 60 algaecide after getting chlorine to 0.0ppm to prevent algae from growing in your pool during the process that might take few days.

    3. Get your pH to 7.2 using pH minus

    4. Put your filter on circulation and add 1pound ascorbic acid for every 10,000 gallons pool to get stains away within 24hours.

    5. Get pH back using pH increaser, then raise TA using Alkalinity increaser since ascorbic acid will reduce both

    6. Add chlorine to raise your FC to around 3 to 4ppm.

    To prevent more stains in future, use metal sequestrant like SC-100 by Orenda Technologies in your water. Find ascorbic acid, Polyqyat 60, and SC-100 Orenda metal sequestrant via different Amazon links here: https://dengarden.com/swimming-pools/Why-Swimming-...

  • My pool is dark green and it’s not algae. What should I use? It is approximately 20,000 gallons.

    If not algae it's, copper metal stain. Lower your FC to 0ppm and put a filter on circulation before adding ascorbic acid, making sure you're targeting stain affected areas. 20K gallons require 2 pounds of ascorbic acid.

  • I have rust stains and dime-shaped black spots in my pool. How do I remove them?

    You need ascorbic acid to do away with the rust. Before adding ascorbic acid, you need to lower your chlorine to 0.0 ppm and pH to 7.2. Leave the filter running and add ascorbic acid (1 pound for every 10,000 gallons). Then get pH and alkalinity back to normal, then finally chlorine. After getting chlorine back to normal, do not shock the pool for about two weeks to allow the ascorbic acid to work well and the rust should disappear gradually.

  • How do I get leaf stains out of a vinyl lined pool?

    Simply scrub the affected spots using a brush, then leave the pump running for at least 24hrs.

  • Our pool tests negative for metals but still every time we shock we get stains... still follow your above instructions or do something else? (I constantly have to use Ascorbic acid after every shock)

    Your pool needs metal sequestrant. You can use Orendas SC-1000 to hold metal compounds so that any metal available will not react with chlorine. Alternatively, you can add ProTeam metal magic to remove metals through your filter. You're are getting stains because your water still has metals in it. Here is more details: https://dengarden.com/swimming-pools/Why-Swimming-...

© 2015 Barack James

Comments

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    • Barack James profile imageAUTHOR

      Barack James 

      3 months ago from Green City in the Sun

      Thanks Connie I will appreciate, sharing is caring.

    • profile image

      Connie 

      3 months ago

      Definitely gonna try this and im sharing. Thanks.

    • Barack James profile imageAUTHOR

      Barack James 

      4 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 

      4 years ago from India

      Very informative hub. Interesting read

      Voted up and shared

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