Bill I strongly suspect that the white deposits that some of us see with many additives are the result of having water temperatures in the 30-40C range. Water wetter and the like have silicates in them that precipitate out between 35 and 60C or so. Above that temperature the silicates exist mostly as polymers in solution. So for automobile coolants it wouldnt be an issue but in our systems it is. Incidentally silicate is what makes your skin feel so smooth if you bathe in hot springs.
Some additives use molybdnate instead of silica (purple ice I think?). It does the same thing.
Most good biocides I use in the lab are going to be bad for copper heh.
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