copper in pools

[Aqua Lab Rat]

When there are blue stains we obviously say it is copper, but copper what? I'm asking partly because I'm wondering if it might form copper phosphate, which is one kind of blue compound. I just helped someone understand what causes copper cyanurate, and that has me thinking about other types of copper stains.

 

[JoyfulNoise]

Blueish colors of copper are copper carbonate. Copper phosphate would be very unlikely to form.

Copper stains on plaster are usually a mix of copper hydroxide (brown color, will be removed by vitamin C slowly) to black copper oxide (can not be removed by vitamin C). Fresh copper stains start off as a mixture of copper carbonate/copper hydroxide and then transition with age to copper oxide.

 

[Aqua Lab Rat]

I assume that high pH and/or high alkalinity make this more likely to form. Are there any other factors outside of carbonate and copper concentrations that make this more likely to form? Thanks for the answer - I learned something today.