You do Not Want Copper in Your Pool Water
You do not want copper in pool water. Yet manufacturers are adding copper to many pool products. Products names or labels that say "Blue" are a hint the product contains copper. Alternative sanitizers and "chemical free" pools--The Truth! discusses why copper is put in pool products.
Copper can only be permanently removed from pool water by replacing the water.
In general, less than 0.5 ppm copper will likely not have much effect on pool water. 0.3 ppm is even safer. Over 0.5 ppm you may have some staining or water discoloration, depending on pH.
What are the Effects of Copper in Pool Water?
- Green to black stains
- Emerald green pool water
- Blonde or gray hair turning green
How Does Copper Get Into in Pool Water?
- TriChlor tablets, sticks, and granules
- Shock products with "PLUS" in them
- Mineral systems
- Deteriorating heater copper heat exchangers
- Rarely from groundwater
How to Test for Copper In Pool Water
Find a pool store that can do a "total copper" test, not just a "free copper" test. Free copper is just the amount of copper ions in solution but does not typically include copper that is sequestered by a metal sequestrant chemical. Total copper uses an acid digestion step which frees up all the copper in solutions and gives you a total amount. 
Copper tests only test for copper in the water. So, any copper in stains or that is sequestered will not show up on a "free copper" test.
How to Remove Copper Stains
Copper stain treatment does not remove the copper from your water, it only removes the solid copper stain from the wall by making it dissolve back into solution. So you still have copper in your water.
Sulfamic acid ([NH2]HSO3) is normally used to remove copper stains. Although it is extremely effective at lifting stains, sulfamic acid drastically affects water chemistry. You find Sulfamic acid in Jacks Magic #2 Copper and Scale Stuff.
The most effective sequesterants for copper are based on HEDP, phosphonic acid, or phosphonic acid derivatives. Some of the top sequestrants are:
- ProTeam's Metal Magic
- Jack's Magic The Pink Stuff (regular)
- The Blue Stuff (fresh plaster)
- The Purple Stuff (salt)
Metal Free is not one of the sequestrants we recommend, it is inferior to the other choices. You can also find other brands with similar active ingredients, some of which are noticeably less expensive.
Sequestrant doesn't get rid of metals, it just holds on to them so that they can't form stains. Sequestrant wears out slowly and must be constantly replaced. The only way to get rid of metals is to replace water with some water that doesn't have metals in it.
Read the copper section Stains in Your Pool for more on removing copper stains.