well your answer lies in here:
http://www.geocities.com/xdigitalchaosx/corrosion/
and a thread that has alot more info about it, but its 9 pages long of us learning wtf was going on:
http://forums.procooling.com/vbb/sho...ght=purple+ice
to make a long story short, waterwetter seems to do a bit better because purple ice seems to separate and make a cloudy film. BUT this was in a standing cup. I still have these tests going and i will take some pictures one of these days. along with a summary of that 9 page thread.