I assume someone has run PurpleIce as an additive - any results with that? According to Royal Purple, it's a synthetic. I was thinking it might not be as harsh as a glycol based solution. Not sure about Water Wetter's makeup, but I know it stunk when I used it years ago in one of my loops! I run PurpleIce in my race car with distilled water and it works well, though I can't speak about long term buildup since it doesn't see constant use (drag car).
By the way, I'm getting back into liquid cooling after 4 years of being on air, so this is a very interesting topic as I get acclimated with the latest techniques.
Tom