I have a 6 gallon nano and just got a Hagen 20g co2 kit with bubble checker. I'm at 1 bubble every 2 min just wondering if that's enough or too much.
1 bubble per two minutes is very low; are you using the Hagen DIY CO2 (with yeast and sugar) kit? If so, I would first check for leaks, and then if you are absolutely sure there are no leaks (double check), then it might be because you used water that was too hot and killed off the yeast.
I have the regulator barely open I can increase but unsure where to be.
You can slowly increase your CO2 rate and monitor your livestock with each increase. For a 6 gallon, 1 bubble every 3-4 seconds is probably a good rate. I used to run ~1 bubble every 3 seconds on my ADA Mini-S (~3 gallons).
Your diffusion method is also important; you could have a much higher bubble rate, but with poor diffusion, not much CO2 will make it into the water column.
Finally, if you use a drop checker with a 4 dkH reference solution, you can also ballpark the amount of CO2 that is being dissolved into the water column.