20oz tanks, but i could rig up a bunch in series, and i can get them refilled for free at work so its not much added cost...

also an electronic solenoid would be a good idea, i think i can get my hands on one for a paintball gun for free, my good paintball gun uses an electronic solinoid, but im not about to scrap that

and yes, the gauge is in PSI

the HARDEST thing seems to be calculating how much co2 is in the room, the sensors are SOOOO expensive... wonder if i can buy a carbon monoxide detector and switch the sensor with a co2 sensor (would cost around 70 bucks to do) but not sure it would work.... if it does, i could rig the alarm to trigger the solenoid to turn off