Co2 Levels high w/ exhaust ON?

This may be a dumb question but this is my first go with bottled co2, I have the Co2 on with a 400 CFM fan on as well in a 1,000 cubic foot room. I have a Co2 monitor in the canopy and it reads from 900-1200 ppm... It is accurate an new of course which also gives me a H/L PPM, H/L Temp, H/L humidity. Is it possible that my girls are still getting sufficient Co2??? the fan on keeps the room at 76-78 degrees.

More than likely the exhaust will be pulling the co2 out of the room. Most ppl use co2 in a sealed room or shut their exhaust off while the co2 is pumped in and just keep the circulation fan on inside. Maybe get a thermostat so the exhaust only comes on when your room reaches a certain temp. That way u should be able to get the co2 ppm's up to an ideal 1500 .