CO2 question. Very high reading without generation??

I have a sealed 8X16' room I'm setting up. I am experimenting with a 35 gallon mini aero system. I have a CO2 system like this, http://www.planetnatural.com/site/co2-control-system-cdmc-6.html, only an older model. Before I put anything in that room, I set it to 800 ppm. and it held right around there. Since I started the aero system, the CO2 doesn't emit at all and it runs at like 1680 currently. Can the air stones in the aero res generate CO2.WTF?? I don't get it. Also, i "read" that excess CO2 isn't necessarily bad, it's just a waste.
ANY help is greatly appreciated. Thank you. Mark

Bump!!! how can the co2 stay so high?

I don't have any experience with that unit, but I would assume
it's calibrated correctly?

I know that plants make co2 in their dark cycles and when lights
first come on there could be a spike in co2 but if it's staying there
full time that just doesn't make sense.

If it really is that level all the time, I think I'm very jealous.