Is it an atomiser or a reactor? Can you post a picture?
this what I ordered, but they sent 1/2" mine takes 3/4"..
I am not familiar with that particular atomiser, some of them require quite a bit of pressure (30-40 psi) to produce bubbles.
A drop checker is what I use to estimate CO2 level in the tank. I must admit that it is not the best way since actual CO2 bubbles can enter the airspace giving higher readings (like 30 ppm CO2 when the tank water has less). Ideally, the drop checker should measure previously dissolved CO2 (like when you use a reactor).
The position of the drop checker (away from diffuser) should minimize the error.
I have a drop checker in my tank now, I was running a DIY co2, but now I picked up a 10# & regulator with silonoid .