Is *everything* else *perfect*?
IE: lights (no CFLs, real lights)
Temps? Can dial in any temp you desire?
Humidity? (see temps)
Plants have no nute burn, no pests, ultra healthy?
CO2 is not for playing with. Too much (only possible with a tank) can kill a plant. Yeast or vinegar will produce far less then optimal levels (aka: playing)
Tank $100 -$150(refills $10-$30)
Regulator $30-$60
Solenoid $30-$100
ppm controler $400-$1000.
I see *zero* reason why hydro is needed for CO2; but open for ideas/reasons.
Make everything else perfect first. Putting CO2 on a start up/learning room is like $3K stereo into a '74 Pinto wagon.
As for the paintball cans? Find a big balloon and poke a tiny hole in it. Fill the balloon and let it slowly leak out. *zero* control, but cheap. (no control=pointless in my eyes.)