Matt Hanson wrote:

I've had a very bad problem over the last few days with my brand new
high pressure CO2 setup. (not DIY!)

I cannot keep a constant bubble going for more than a few days at a
time. Here are the factors that I have eliminated:

(snip)
BTW - for what it's worth, I have one of those "needle valves" from Home
Depot. I'm already starting to suspect the problem might be somewhere
there. It's not even really a needle valve, so the control is less than
desireable. I'm not quite sure how they can even be marketed as a
needle valve. Tell me folks, is it in the valve?

Your suspicion is correct!