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!
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.
Here's how to prevent metal stains:
Two more things to keep in mind:
If it's too late & you already have staining: