...an experience I just went through, you can learn from.
I bought a greenair burner, and monitor for an air-tight room 8x7x7, right. I hook it up, the burner comes on, ppm gets to 1600 then shuts off. ( the piolet light stays on) Mine has a light sensor on it so....it shuts down when the lights are off (plants don't absorb co2 while they sleep, they make their own then)....anyhow....when the lights came back on, my ppm was like 2000 ppm!!!!!! The damn piolet light got it that high! Now, I'm not even running my burner....and my ppm is always 2000 ppm. I made sure my monitor wasn't faulty by taking it outside to get a 400 - 500 ppm reading. I thought damn, should I have just bought a candle??? WTF????
...if done over again, I wouldn't have got a co2 burner, but the monitior is essential. Improvise for co2 production, or get a co2 tank and regulator. Good luck.