I looked into paintball guns at a big sporting good store near me - $.30 for 20 oz is pretty cheap. Are you sure it's not $.30/oz? The tank itself was about $50 and I saw refills for about $5. Maybe you could hypothetically belong to a paintball club and you're the "refill guy" (wink, wink) It could get hard to explain if you're back there refilling a bunch of canisters every week or two (and not buying anything else), esp. since the little 12 gram cartridges fire off something like a hundred rounds of ammo. Is that right? That would have to be a damn big paintball club. That much CO2 could supply Paintball World War III !!
I think the hard part is figuring out how to let the gas out of the tank in a regulated way. I haven't matched up the tanks to a hydro regulator/solenoid. It would be interesting to see if they'll fit or if they need an adapter, if that even exists.
In an 8x8 grow room, you would need about 5 1/2 canisters a week to maintain optimal enrichment if you grew 24/7 in veg (obviously cut in half during flowering, since enriching at night is pointless). You'd have to figure out how to regulate the canister so that the gas escapes evenly over a period of 30 or 60 hours respectively. Ideas??
The soda/beer tap tank idea is still good, although the logistics of it are going to be hard to work around for the average person who doesn't have a sympathetic buddy who works in a bar. You can't just buy these things at the package store. It might be hard to explain the Miller Lite or Pepsi truck rumbling up to some kid's studio apartment... :laughing:
~cb
[clarification] There is some evidence that photosynthesis in large plants continues for an hour or so after dark, so the plant could still use some CO2, but the amount left over in the air should be more than adequate.