How big is your tank? I have a 55 gallon and am trying to figure out how many to make, one or two.atmmachine said:What I did was make a small hole in the lid of a 2litre pop bottle. It's small enough so when you shove the piece of air-line tubing through it creates a seal. Then add 2 cups sugar, half package of baking yeast(1teaspoon), I use red star, then add 1/4 teaspoon of baking soda. Then add warm not hot water and fill the bottle up to below where it starts curving. Then put the lid back on and connect a check valve to the airline and you can diffuse it with a diffuse online or put it in the intake of your filter and it will be chopped up with the impeller. Should last about 2-4weeks. Can buy a kh and gh test kit to know the ppm and water hardness. Monitor your pH and make sure it doesn't go out of wack witht the co2. Change the mixture every 2-4weeks or whenever the bubbles slow down and keep an eye on your bottle, will have to replace tubing and other parts over time.
That's basically a common recipe all over the internet and forums so I did not come up with it.