A strange buildup issue

Here's one I haven't seen before, and am looking for some help dealing with.

A client has been running a machine for a while on a waterline that has some sort of previously-unknown contamination issue. I have no idea what the contaminant is, but the water measured 400ppm TDS vs 53ppm typical for our area. The water is softened and also filtered through a chlorine/sediment cartridge. It tastes terrible - metallic and mineral.

The original complaint was for problems that I traced to the boiler, heater, and heat exchangers having a significant buildup of a blue-green crust. I have the machine on my bench now, and tried a couple of soaks with Dezcale today and it didn't touch it. Will try something more assertive tomorrow, but I'm not optimistic.

Like I said, the crust is blue-green. What little did dissolve into the descale solution turned the solution a strong Windex blue. Just for fun, I held a small chunk over a lighter and it turned the flame green. If my old memories from chemistry serve me, I think this suggests some sort of copper?

Any thoughts about what I may be looking at here? Or what I might use to remove it without damaging the copper boiler and pipes?

Thanks!

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