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How to Remove and Prevent Metal Stains in Swimming Pools

Brown metal stains on pool stairs

Brown metal stains on pool stairs

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.

Oxidized iron turns pool parts and water to a brown or rusty color, 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 to water, oxidizing these heavy metals to produce different stain colors, 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 fiberglass surfaces
  • across the steps or on various pieces of pool equipment

In this article, we will break down how to:

  • test the water for metal stains,
  • get rid of metal stains in five steps, and
  • prevent staining in the future.
Metal stains before and after removal

Metal stains before and after removal

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 of its metal staining. Green or black stains might indicate metal stains, but they may also occur due to 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 a metal stain and not algae.

Get 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 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 effectively fight and prevent any 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 acids to clear metal stains and may also contribute to more metal staining, which 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 clearing stains takes longer.

3. Run the Filter and Add Ascorbic Acid

  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 you get your pH and TA out of balance by mistake or 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 the 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 pH levels and chlorine will definitely precipitate any metal compound in your water if not treated (sequestered) or removed out of your water.

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 the CuLator metal eliminator was available, there were no practical ways 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 metal level in your water and is replaceable once worn out.

However, the easiest way to avoid stains in your pool is to avoid filling the 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.

Moreover, you need to be careful with the chemicals you add to your pool since copper may find its way in your pool from chemicals such as algaecide or ionizer—and 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.

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. It's one of the most effective calcium and metal stain reducers on the market, and I prefer it when fighting high calcium levels, calcium build-up, and scales, both in harsh chlorine-based pools and saltwater pools.

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 from pool surfaces and prevents metals from staining pool surfaces when chlorine is added.

Moreover, this product improves the life and functionality of salt chlorine generators by preventing scaling, which extends salt cell life and stops calcium build-up before it starts. I specifically recommend Orendas SC-100 for saltwater pools that have metals, scales, and calcium build-up.

Orenda SC-100 should be added in an initial dose for better results and frequent maintenance doses to keep heavy metals from your water.

For the initial dose, 1 quart per 10,000 gallons should be added when the pool is full. For maintenance doses, 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 Sequestrate in Your Pool Water

Metal sequestrate should be the last option to use in a pool because it works differently from metal removers like Metal Magic and Orendas SC-100. Metal sequestrate does not remove metals in your pool water. Still, it naturally binds to 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 to 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. Therefore, they should be introduced regularly in your pool water to maintain the right level to keep stains away.

The most effective sequestrants are derived from phosphoric acid, and the best in the market today is Pool Mate Metal Out. This product helps prevent discoloration of pool water from iron, silver, manganese, copper, and other metals and minerals that may be present in the water supply.

Pool Mate Metal Out is an excellent general-purpose sequestrant that 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 weekly, 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

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

Answer: 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:

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

Answer: 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.

Question: My pool turns green, the Shock-It turns it brown. What do I do?

Answer: You have Iron metal in your pool and that's why your pool turns brown when you shock it. Use Ascorbic acid to clear the stains and consider draining and refilling portion of your pool water to lower metal levels or use metal remover like ProTeam Metal Magic to remove metals through the filter.

Question: Is It necessary to use a sequestrant right after using Ascorbic acid?

Answer: Yes, you have to use a sequestrant or any metal remover to prevent metal stains. Ascorbic acid only works to clear metal stains.

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

Answer: 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.

Question: How can I remove copper from my pool?

Answer: You can add Proteam Metal Magic in your water to treat metal stains and remove Copper and other metal compounds through the filter. To avoid metal stains, monthly dosage is required to remove metals from your water. You can find it on Amazon through a link in the same post.

Alternatively, you can use CuLator Ultra PowerPak in your skimmer or pump basket to remove metals before entering your pool. I prefer CuLator because you will not have to worry about adding a metal sequestrant on weekly or monthly basis.

Question: We have an ionizer but this results in green staining around our liner pool (and swimming costumes turn green) - so most of the year we put chlorine in the pool which keeps green staining away. But recently we had brown staining on the pool liner which was removed with ascorbic acid but the brown staining has returned. Is this because we are using chlorine and ionizer is present (as the water still goes through ioniser chamber even though the ionizer is not switched on)?

Answer: The brown stain might be caused by the ioniser that deposits Iron metal in your pool, you need to clear the stains using ascorbic acid, then consider reducing iron metal levels in your pool by draining and refilling a portion of your pool water or use a metal remover such as ProTeam Metal Magic to remove metals through the filter and avoid brown stains when you shock your pool or when pH is low.

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

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

Question: Is CuLator really a good product? I think I have a metal stain problem which keeps coming back every few weeks after I treat it with ascorbic acid, even though I keep Ph level just a bit lower than normal. I used it last year, and the little pouch just kept swelling, and the gel oozed out. I didn't see any change in pouch color as it said in the instructions.

Answer: I guess you are using Well water. The best way to do it for a trouble free pool is to pre-filter your water before it enters the pool system.

If your pool is near your house, you can pass water through the kitchen filter system and pipe it to your pool.

Alternatively, metal CuLator can work very well by removing all types of metals from your water; I use it on Skimmer with skimmer bucket.

This is optional, but you can add Metal sequestrant inside your pool to hold any small amount of metals that may cause more problems like oxidization when chlorine is added.

Here is more info:

Question: 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)

Answer: 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:

Question: My pool has various blue stain areas, especially on the steps. The pool maintenance company says my heater is disintegrating and putting metal in my water. He says I will need a new heater and acid wash. My plaster is only 2 years old. Does this diagnosis of my pool's discoloration sound reasonable or should I get a new pool maintenance company?

Answer: Use ascorbic acid tablet to test if that is a metal stain. Rub ascorbic acid tablet against the stain and if it comes out or loosens its metal stain. I am not sure if the heater is causing the stain but you can test your pool fillwater for metals. If your pool fillwater tests positive for metals you can metal magic (sequestrant) to remove metals through your filter. Ascorbic acid will clear all the stains.

Question: How can I get a purple stain out of my vinyl liner pool?

Answer: Purple stain is caused by a mineral called Manganese. That means your water has Manganese in it. First of all, you need to add more water in the pool to cover all affected areas. Then carefully reduce the pH level to around 6.8, this is necessary since you cannot do away with Manganese stain when pH is high. Finally, do a thorough brushing starting with affected areas. Thorough brushing once a day for 2 days should clear all the purple stain. Clean your filter to remove any Manganese debris remaining, leave pump running for 24 hour and then restore pH level to be between 7.4 and 7.6 by adding pH plus, and finally balance all the other chemicals in the pool.

© 2015 Barack James


Barack James (author) from Green City in the Sun on July 12, 2019:

Thanks Connie I will appreciate, sharing is caring.

Connie on July 12, 2019:

Definitely gonna try this and im sharing. Thanks.

Barack James (author) from Green City in the Sun on July 08, 2015:

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

JR Krishna from India on July 08, 2015:

Very informative hub. Interesting read

Voted up and shared