Hey guys - from my post above:

A caveat here - I recall that I did find bits of tissue in my GPU blocks (probably residue left after painting the radiators), so can't rule that out for sure. Although I do see what looks like crystal growth, there is some fibrous stuff.
As I said, there is some residue that is obviously not related to any possible tissue bits - I'll show pics of the reservoirs later. But again, this wasn't so bad that I would vow never to use the stuff again - just would be much more careful. That said, I think distilled water is easier for long term use And to kgtiger - yes, I have silver coils that I will use when I do my next clean loop.