For CO2 i use 1/3 approx. cup sugar, 1 package quick rise yeast (for bread making), put it in a pop bottle, add some lukewarm water, shake it up. The yeast eats the sugar and the byproduct of the yeast eating the sugar is large amounts of carbon dioxide. Make sure you leave about 1/4 to 1/3 of the bottle empty because the yeast will 'foam' up. I leave the cap off of mine, but alot of people put a hole in the cap with a little rubber hose in the cap going to the plant.
IMO i prefer to have my co2 ABOVE the plants iff possible ( i put mine on a closet shelf at the top) because CO2 is a very heavy gas. it falls and settles at the bottom of whatever its in. By placing them at the top, imo i feel like they get a better PPM of co2 in the air that way because it gets circulated by the small fans. A bunch of co2 at the bottom of your room sitting there while the lighter air blows around over top isnt much use. It need to get to the leaves for the plant to use it. Most plants can use many many many times the co2 that is available to them naturally, as a result of plant evolution when co2 levels in the air were higher.
I use 3 pop bottles on a top shelf. Lasts for a couple weeks, smells like baking bread. get rid of it when it smells like booze.
BTW i definitely noticed a difference in rate of growth after i added co2.