Before we go on...
I have to put up a link to another thread here, where
DigitalChaos compares Redline Water Wetter and Purple Ice. .
There's 8 pages, but throughout all of it, you'll see a pattern, and some solid info.
But it's not the complete info we're looking for.
The question comes down to how many different metals you have in your rig.
1- Copper and aluminium
2- Copper and brass (yes, those barbs)
3- all copper, or all aluminium
I'll have to re-read the whole thing again, to summarize it all, but the options are:
a- Distilled water only
b- 2 oz of Redline Water Wetter per gallon
c- 4 oz of Redline Water Wetter per gallon