you have a line leak somewhere between your gauges and the valve inside the welder. I recently built a new cart and was able to shorten up the line. I got rid of most of my leaks but by cutting the wore out ends off the lines and reclamping them. Since your is new, I would make sure the gas attachement/regulator-valve in the welder is hooked up right. To completely drop a tank to 0PSI during dinner it would have to be a big leak. I've went from 7,000PSI to 5,000PSI overnight.
Yesterday I went out to weld in my sliders and it was still at open /forums/images/graemlins/yikes.gif /forums/images/graemlins/doah.gif but it was still at 5,000PSI and it has been open for at least two weeks since I've used it last /forums/images/graemlins/peace.gif
Also, I run 25PSI at the gauges it usually drops to 21-23PSI during welding and it seems to do well set right there. But always anytime your not using the welder for even 10minutes aways close the valve on the tank jus tto prevent leaks like this. Just like I said above though, I sometimes forget to close the valve the tank /forums/images/graemlins/doah.gif Before I changed out the lines I've lost 3000PSI overnight before /forums/images/graemlins/dunno.gif at $17 a tank its not hard to start remembering to close the valve /forums/images/graemlins/whistling.gif