KillerRain,
Thanks for your interest. The degradation of the copper is very apparent in my tests. There is a lot of very fine copper film sluffing off the walls between the two sets of opposing tubes from time to time. It just blows out the top of the stack with all the bubbles.
I previously forgot to explain why I was using the copper tubing. First off, let me say that I can purchase the stainless tubing for less than the copper tubing from Verocious Motorsports. The primary reason that I'm fooling around with the copper tubing, is that it's much easier to machine and work with. Therefore using the copper tubing will help speed up my cell prototype building. Once I have a prototype doing what I want it to do, I'll then build a real cell with stainless steel tubing and/or plates whatever the case may be.