Copper sulfide?

The sulfur can come from any number of sources. In my case it's usually hydrogen sulfide from the bacteria in the aquifer (I have well water). I can actually smell it sometimes in the late spring and summer. Smells like rotten eggs. Although the odor is offensive, it's harmless. Anyway the hydrogen sulfide apparently reacts with the copper and somehow you end up with copper sulfide.

Also, you can get some sulfur (sulfur dioxide) from your cane sugar. Perhaps you changed brands? Or the manufacturer/distributor changed its source? Could be any number of things.

Or perhaps it's time to acid wash some of the copper in your system. A little citric acid, lemon juice, etc. with some water does wonders.

I guess it's possible that it has always been there, but your process of diluting early prevented its formation (crystallization) ... especially if there's any chlorine in the water you're using to dilute with.

My chemistry pretty much sucks once I'm beyond the basics ... but, I do know that a little chlorine will cause copper sulfide crystals to precipitate. Many homes in my area have these chlorine traps (I believe that's what they call them ... they look like basket filters) but you can add chlorine tablets to them. The idea is to eliminate the copper sulfide close to the source to prevent particles and that occasional rotten egg smell. If you can isolate some of those particles and put them in a clear glass of pool water ... and they go away ... then you can be reasonably sure of what you're dealing with ... then work the problem backwards.

Sorry for so much hot air ... figured you'd prefer more info than not enough.

Regards,
--JB