So I have looked into SPT...the viscosity is high which is a bummer. There is also LPT it is less viscous so that's encouraging...BUT...the problem with both is they say "REACTS WITH COPPER" in my application there can be small copper dust particles so I'm wondering...what is the reaction? What would the reaction be?
I think you might be confused a bit about viscosity numbers. A moderate concentration SPT solution would have a low viscosity of only a few centipoise and even a high concentration solution would only be around 10 cP. While these numbers are several fold higher than water you would not readily notice the difference. It would probably be better for our intuition if viscosity was reported on a logarithmic scale like decibels. Anyways, milk has a viscosity of 3 cP which is probably a bit above what SPT would have with a specific gravity of 1.45. On the other hand, a sugar solution at such a density would be a syrup with a viscosity higher by a couple orders of magnitude.
As for tungstate's incompatibility with copper presumably the copper just replaces the sodium and the resulting copper tungstate wouldn't be soluble. You would almost certainly have the same sort of problem with most non-alkali metal ions. This is not a significant problem for your application unless you somehow have large amounts of
dissolved metal ions. The copper is not going to be dissolved unless your pH is acidic and I doubt that the tungstate would be soluble at acidic pH.
You would have no such problems with chlorides or nitrates. These anions are highly hydrophilic and form many deliquescent salts. I picked calcium chloride because it was deliquescent and its two ions are unequivocally benign and it can achieve an SG just barely above your stated number. Calcium nitrate would be able to get a higher SG than the chloride and while nitrate isn't something we evolved to consume in large quantities, it isn't particularly toxic.