Metal Stains & staining

Iron, Copper & Manganese Stains in Swimming Pools

Metal Stains are the third most common problem in swimming pools.

The problem is most people don't realize they have metals in  their water.  Even trace amounts of these metals (iron, copper, manganese,  cobalt, silver) can cause staining. In fact there's enough copper in ONE penny to completely stain an average sized swimming pool!  Obviously, the conditions have  to be right.  This is where prevention & good, proper pool care come into play.

Here's what happens: metals come into your pool whenever fresh, make-up water is added.  These  metals are already dissolved in the water.  Whether you use municipal water or well water, metals  can be present.  

As the metals accumulate, the greater the chance that they will eventually come out of solution.  Once out of solution, they make the water cloudy or worse, they  "plate out" on the pool's surfaces & leave a stain.  Metals can come out of solution through a variety of ways.  But there's 2 ways that typically cause this to happen. 

The good news is that metal stains & staining is preventable and when they appear, we can make them disappear.

Iron and copper staining. Preventable? Yes. Treatable? Definitely!
Iron and copper staining. Preventable? Yes. Treatable? Definitely!

What causes metal stains

Simple causes of staining.

Metals can always be present in water; any water.  Here's why these metals stain.

The first way metals come out of solution and stain is when a pool is shocked whether with chlorine or a non-chlorine oxidizer, the shock oxidizes everything in the water, including metals.  Oxidized metals become "rust" in the case of iron or "Verdigris" in the case of copper.  

The second way metals come out of  solution or are left "exposed" when the pH, Total Alkalinity and/or Calcium Hardness are left unchecked & allowed to go low (pH below 7.2, Total Alkalinity below 80 ppm [non-Pristine Blue pools], Calcium Hardness below 100 ppm).  The water becomes aggressive & the metals are more susceptible to oxidation. In  many cases, pool-owners don't properly test their water & more likely rely on  the "look" of the water (the water's clear, everything must be alright). 

This  is typically the case with blonde hair turning green - low pH helps bring copper out of solution & "plates" it out on the person's hair!  Then people blame the chlorine! It's not necessarily the chlorine, it's the copper in the water.


When it comes to testing, remember that you can only test for metals when they are in solution.  Once oxidized, the metals come out of solution & cannot be tested.  That's why once a metal stain has  occurred, the metal test will NOT show any metals present.

Iron staining (rust) from a corroding pool wall or light niche.
Iron staining (rust) from a corroding pool wall or light niche.

preventing metal stains

Metals stains are completely preventable

Here's how to prevent metal stains:

  1. Have the pool water professionally tested regularly: at opening, mid-season &  at closing (at least) & make sure they do a copper & iron test. 
  2. Keep the water balanced. pH 7.4 - 7.6; Total  Alkalinity 125 - 150 ppm (vinyl pools), 80 � 125 ppm (plaster / gunite pools)  (Please note that these TA values ARE NOT applicable in Pristine Blue treated pools where the TA is to be maintained at no higher than 80 ppm); Calcium Hardness 200 - 250 ppm (vinyl pools), 225 - 275 ppm (plaster / gunite pools). 
  3. Prevent metal stains by using BioGuard Pool Magnet or Jack's Magic (a sequestering agent) when filling the pool then adding a maintenance dosage monthly. Sequestering products will NOT remove the metals from the water, but they will prevent them from being easily oxidized.
  4. To REMOVE metals (ionized, dissolved metals) from the water,  CuLator is an excellent product that easily traps & physically removes heavy metals such as Iron, Copper, Manganese, Silver, Cobalt, Nickel and Lead.  Simply place the CuLator pouch in your skimmer or pump basket - depending on the  product - and allow the CuLator to work.

Two more things to keep in mind: 

  1. If you have well-water, treat the pool water automatically & immediately. 
  2. If you have municipal water, Pool Magnet won't hurt.  


Treating pool metal stains

Once the metal stains have appeared

If it's too late & you already  have staining:

  1. Get the water balanced.  Keep in mind that further discoloration COULD occur.  This is a temporary phenomena & will clear once the treatment process is complete.
  2. For light staining of iron & copper, use BioGuard Pool Magnet at a rate of 1 qt. per 10,000 gallons of water.  BioGuard Pool Magnet works well  on "fresh" stains. Avoid shocking the pool for about 3 days. The Chlorine level must be less than 2 ppm for Pool Magnet to work effectively.
  3. For  heavy staining, Jack's Magic Blue Stuff is an excellent product.  We like Jacks Magic because you can have high or  higher amounts of chlorine present (in excess of 10.0 ppm). This is especially useful when treating a combined problem of metals & algae.
  4. Heavy metal staining on vinyl, fiberglass or acrylic steps can be treated with Jack's  Magic Step Stuff.  
  5. Save yourself time, money & effort using Jack's Magic Stain ID Kit.  It really helps in identifying the exact metal that's causing the stain.
  6. Use products such as BioGuard Sparkle Up or CuLator to physically remove heavy metals from the water.