haven't welded for a couple of days and got a new tank of argon and hooked it up today, tried to weld a tab on an aluminum tank i built and there was black crap and it was welding like i didn't clean the aluminum at all. I tried it on some new clean 6061 stock and there is no white ring around the weld and still black crap in it? I tried new tungsten, gas lens, acetone on everything including the filler after stainless wire brush. I tried everything from 10%-50% ac balance and nothing? could this be bad gas? I also tried changing flow from about 5cfh-20cfh I wouldn't think bad gas would make the ac cleaning disappear?

Machine is 250ex, about a month old, haven't had a single problem yet and machine is welding perfectly, here is the last weld i did before switching out the bottle.