To those people who are using Up New Atomizer system (D-508 series) or similar, pic below, do take note on the CO2 safety nuts. It is quite weak, I have 3 atomizer and all of them are broken as seen in the picture below. You can clearly see the top part is broke.
I do see the nuts for newer mode D-519 series, the top part, have thicker plastic construction. Unfortunately I cannot use it on D-508 series due to different diameter.
I email up-aqua support about my problem and they going to send me replacement nuts. Thank you for the great support.