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How to Remove and Prevent Metal Stains in a Swimming Pool

Updated on August 21, 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 Swimming Pool Metal Stains

Swimming pools with water sourced from a well are fond of developing metal stains due to metal compounds such as Iron and Copper present in well water. Metal stains or rusty brown or dark stains in swimming pools normally occur when pH and Chlorine are out of balance.

This article including the video at the end explain how to:
1. Test for metal stains
2. Get rid of metal stains in 5 steps
3. Treat pool water with metal compounds and
4. Remove metal compounds in your water to avoid metal staining.

Precisely, metal stain problems are very common in pools with lots of metal components in the water. Metal stains come in different colors including: Black, green, rusty brown, orange, and yellow; which may occur on different spots of the pool such as:
1. Bottom or walls
2. Along vinyl liner
3. Fiberglass pool surfaces
4. Pool steps and
5. Various parts of pool equipment

However, the pool water should still remain clear and not cloudy even if metal stains are present. In most cases, murky or cloudy pool water is not associated with metal stains.

A) Testing pool Water: Metal Stains or Algae?

Before taking any action to treat discolored pool water; you need to be certain of the cause: It could be algae or metal stains since not all green, yellow, or black stains are caused by metal stains, but may occur as a result of algae.

If you suspect the stain is caused by iron or any metal compounds in the pool water, try Vitamin C test. Vitamin C test uses ascorbic acid to identify metal stains: Hold vitamin C tablet against a potion of stain for about 30 seconds.

If the stain vanishes or lightens, then it is metal stain and not algae: Having identified the stains as metal stains; it is time to get rid of them using ascorbic acid.

B) Getting Rid of Metal Stains in 5 Easy Steps

Step 1: Lower Chlorine Level to 0.0 ppm

Before adding the 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 and it won’t work for you in removing metal stains in the pool.

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.

Step 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 causes metal staining and that is what you need to get rid of.

Step 3: Run Filter and Add Ascorbic Acid

Put your pools filter on circulation if it's not on: 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.

Using a tin or a cup, drop the ascorbic acid down the sides of the pool while going all round the perimeter of the pool.

Let the ascorbic acid circulate for around 30 minutes; and watch how the metal stains fade away before your eyes.

If you still see some small stains after 30 minutes, add more ascorbic acid on the spots you still see the stains while the filter is on. Leave the filter on 24/7.

After 24 hours, all the stains should have faded away. Start re-balancing your water chemistry after 24 hours.

Step 4: Getting pH and Alkalinity Back to Normal Levels

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

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

If your TA is within the recommended level but you still need to raise your pH, you can use borax to raise your pH to 7.2. Borax may have small effect on TA but not like soda ash.

Step 5: Getting Chlorine back to Normal Levels

After getting pH and TA at recommended level, it is time to raise your free chlorine level of 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 metal staining in the process. If you have Cyanuric acid in the pool, 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 be more accurate on the level of free chlorine your pool needs to avoid any further metal staining.

After getting chlorine to recommended level, avoid shocking your pool for about two weeks to allow ascorbic acid to be completely used up: After about two weeks, you will notice chlorine being used up in the pool like usual: You can then begin to shock your pool carefully watching not to add excess chlorine.

Important: High levels of pH and chlorine will definitely precipitate any metal compound that is not treated (Sequestered). So, how do you treat pool water with metal compounds to avoid staining?

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

C) How to treat Pool Water to Avoid Metal Staining

After adding ascorbic acid and all the chemicals including pH, alkalinity, and chlorine are all well-balanced, the only possible solution is to prevent metal stains from forming in the swimming pool by treating the pool water using a sequestrant.

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

How does this happen? Sequestrants naturally bind to the metal, preventing them from depositing as stains in the pool water.

The most effective sequestrants are derived from phosphonic acid and my best option is 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 and you need to add it more regularly to maintain the correct levels in the pool water for it to be effective.

Finally; I just thought you should know: Using borates in metal laden pool water may be useful in avoiding metal stains since borate ensures:

  1. More stable pH by prevent pH drifting
  2. A reduced chlorine usage since it act as a sanitizer

Goodluck and happy swimming!

D) How to Remove Metal Compounds from Pool Water

Some years back before CuLator metal eliminator was available, there was no any practical way of removing metallic compounds from pool water, and the only possible way to get rid of metal compounds in the pool was to completely drain the water; and then replace it with fresh water that has no metal components - lots of work it was right?

To effectively and completely eliminate metal compounds in your pool water and prevent metal stains, use CuLator metal eliminator in the skimmer or pump basket, which should work up to 30 days or longer depending on the level of metal in your water.

As such, before actually building that pool; it is always very important to test the source of your pool water for any metal content and avoid water source with metals in it at all cost since maintaining a pool with metals in the water is relatively hard and expensive.

Other form of metals that may be present in a pool water causing staining are Copper, Manganese, cobalt, Nickel, and Silver; which can all be removed using metal eliminator I just mentioned earlier. However, copper may only find its way into the pool from chemicals used such as algaecide, ionizer, and from eroded pool parts with copper like heated exchange coil when pH gets lower than 7.0.


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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