Copper Oxide? Help me get rid of this.

[TheMash]

My Apogee GTX got the same green build up over time inside the waterblock. Only copper was used in the loop. Like you, I was using just distilled water. My tubing did not turn green, and the water was clear. Soaked the thing in CLR to clean it off.

Hi
Well Im not alone
Btw, I used deionized water, not distilled. And it was not so deionized I think.

Sorry for ignorance, im italian, but what is CLR?