1 gal jug, luke warm water, you dont want HOT water it will kill the yeast.
add 1 cup sugar and fill gal jug 1/2 way with WARM water....shake..
poke a hole in the cap of the jug, run a aquarium line up behind your circulating fan......
this isnt going to give you crazy amounts of Co2 but it will let off some and it will give you more than what you previously had which is better than before right?
if you want to measure the levels of Co2 you will need to get a tank, regualtor and a unit that measures the Co2 lvl and releases when it gets below your desired level...this is some $$$ though.
they have a few cheaper Co2 generators on amazon that come in the form of a pad that you hang up and mist...not sure if that interests you or not