When the cannabis plant came to earth about 250,000 years ago the CO2 levels from what I read were 2500ppm. I have read amounts over 2500ppm are non usable to cannabis, but true enough can sufficate pests. I dont know how long mites can go without oxygen for. I would figure they would die quick. 5000ppm and above would make sense to me to kill the pests but I have never tried it. As long as the fans are off the level of co2 would be much higher on the ground so one may not have to use as much.

Reaper: I had a 20 pound tank that I hooked up with a broken regulator. The entire tank leaked into the room within hours. No bad effects where noted. I know testers can be expensive. They sell one use testers for twenty dollars if you want to test the level once at 15mins of a open tank with your room dimentions. You can also make co2 with yeast and sugar but not at levels high enough to kill pests.

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c