I have brass in contact with the buffer at one point in my system, and have noticed that it is getting darker over time. What kind of metals are in contact with the buffer in your systems? Brass? Stainless steel? Aluminium? Does anyone know how it is effected by the buffer, and how it effects ETC?
I was actually thinking about the buffer circulation as a whole - I'm guessing that most people's pump/water circulator will be stainless steel?
I'm also using a heat exchanger from a car to cool the buffer (heat exchanger is aluminium, so that's one more metal..)
Conclusion so far is that air, nitrogen or oxygen doesn't seem to make any difference, brass is ok but aluminium turns the buffer yellow.
Also had trouble with my pump - it was a cheapish circulator for heating systems made out of cast iron and painted on the inside - it gave of a nasty brownish color that naturally spoiled both buffer and tissue quite quickly..
My current system is built around a LKB Bromma 2219 Multitemp II (about $500 on ebay). It can run for a week without a n y discoloring of the buffer (haven't tried longer). As far as I understand stainless steel is the only metal in contact with the buffer.
Hoping someone can learn from my mistakes