well i was in the store, buying a couple things that i will need to start my grow soon, and dry ice caught my eyes. its pure frozen co2 and when it melts, it turns into the gas c02 in highly concenttrated ammounts! dry ice over here runs for $2/lb which is fairly cheap, and can last a while. use some and store the rest in the freezer. heres what you can do dry ice is sold at grocery stores, some food retailers may also sell it. Get your dry ice, and if you dont have any containers at your house, grab a styrofoam cooler! they cost what a dollar or two at max. so now you have a system for co2 for under 5 dollars, a pound of dry ice will normally last for about an hour in water. some places offer dry ice in bulk for super cheap like 10-20 cents a pound if you buy alot. now fill your container, which can be a cooler, 2 liter bottle, soda bottls, anything that can contain water! put it next to your plants, drop your desired ammount of dry ice in the cooler/container, it will produce a c02 smog your plants are sure to love, and if your grow room gets hot, this will also cool it down as the fog created has a slight coolness to it. this isnt a constant supply method of getting co2 but for short burst of highly concentrated doses, it will be beneficial. but if you have the money then by all means buy a ton and keep it going as long as you want i havnt had the chance to actually try this my self yet, becuase i dont have any plants as of now, but id imagine this would be effective. forgot! So you dont blow a hole in your wall, or destroy your pant, if you use a 2 liter bottle, or any plastic with a air tight lid, do not put the lid on, it will turn into a bomb.