ambient here is 370-410 IIRC when I was first setting up. (5100ft) I think mine is influenced by something local, making it a bit higher. I think next time I turn it off for 2 weeks I'll bring the sniffer to my desk and watch it for a few days.

I felt like I was pissing in the wind w/out a sniffer/controller setup..

I have mine to kick in at 1200ppm and turn off at 1550 ppm. humidity of 80% dumps room air. Temp of 92 dumps room air (considering turning this up to 95). A photo sensor won't let it add co2 at night.

For me, my vegging plants are always way ahead of the flowering plants. I want to start 12/12 with them smaller. (they are going in at 5ft now) I already only use t8's and have ppm's dialed back to 700... so CO2 just isn't needed in veg for me. ymmv.