Bubba Kush - Grandmommy Purp

Scrog working well. Pistils finally appearing. Could use some advice on my CO2. I feel like my room is pretty well sealed. Magnetic strips on left and bottom side (permanent seal on right). My fresh air is constant, on low, and colder than the grow room, at around 70F. I have it blowing in at floor level. As you can see in the pics the fans are pointing up into the canopy. The CO2 emitter hose is attached to the back of the wall fan. My theory behind it was that the CO2 would rain down onto the canopy from above as the fan is directed just across the canopy to ensure it reached the Gmommy Purp on the left. Once it falls through the canopy, the cold air layer at the bottom-combined with the upward directed fans, would push the CO2 back through the canopy, and cycle again. My CO2 system engages at 1200ppm, still it steadily falls to around 1100 and begins climbing. The system shuts off at 1250ppm but still climbs to around 1600ppm, hovers for around 15 seconds, and steadily falls again. Total time the system runs is 2 min, every 5 min. It seems excessive and Ive already been through ~40lbs of CO2 in approx 16 days. Any thoughts are appreciated. (BTW my controller does not have a photosensor. So I have it controlled by Alexa to run on the same routine She runs my lights on. Which makes setting the CO2 impossible as it resets on power loss. Im happy with the presets but just giving all info) Ran Florakleen flush for 2 hrs between nutrient change.