Hey NoSaint, congrats on the veg!
If you swap the milk carton for a 30 gallon container and use the garden hose, (airline pipe is a bit small in diameter), Then empty a 2Lb bag of tate and lyle with preferably a whole block of live yeast (not powder), and not to forget the bowl of water to check the reaction effectiveness, you will get readings of between 800 and 1000 ppm. (More than adequate)
It has been said that yeilds can be improved by 25% with those levels of added CO2.
If you havent got a meter then heres a link
http://http://sensors-transducers.globalspec.com/Industrial-Directory/co2_detection this is an all in one bit of kit for humidity, temp, and of course Co2.
Good luck mate, not too long now!
Cheers
EDIT: If you add the yeast as a 1000g block, (couple of quid), then break segments off every few days you will get a retard release and can make the mix last 2-3 weeks with a final heavy mix at the end, before the CO2 bubbles stop....well...Bubbling. Rather than me going into all the science of why it works, google it and see for yourself because its a bit of a shame that you arnt excited about this
)...
Cheers dude.