DIY CO2 is a matter of taking Yeast and Sugar, and mixing with water to create a reaction byproduct of CO2. This works extremely well for 1-30 gallon tanks. For tanks larger you must create more bottles, to increase CO2 output, but it can be done. It just requires more effort, and most tend to go over to pressurized because the time and effort, and added cost over time required. But it can be done. Equipment: Gatorade, Apple Juice, or Oceanspray Bottle 2 Cups of Sugar 1/4-1 teaspoon of yeast 1/4 teaspoon of baking soda (optional) Diffusor: Hagen Ladder, sweetwater AS10, or through filter intake Recipe: 2 Cups of Sugar 1/4-1 teaspoon of yeast (the more yeast the faster the reaction, more CO2 for shorter period of time (2+ weeks)). 1/4 teaspoon of baking soda (optional) Making the Canister (Reaction Bottle): Take drill bit or hammer with a small nail (smaller than the diameter of tubing). Unscrew your cap, hammer the nail in the cap to make a small hole Get some Airline tubing and pull it through the small hole with pliers. The small hole will create a seal around the tubing so no need for glue. That's why you want the hole to be small. Add the Recipe: Add 2 cups Sugar Fill the container with water up to 3/4 way. Add 1/4-1 teaspoon yeast Add 1/4 teaspoon (baking soda) Put the cap on and twist it on tight. Insert the airline tubing in your intake of your filter, hagen ladder or sweetwater stone AS10 from aquaticeco.com. Wait a few hours and you got CO2 Special Notes: Diffuser For the sweetwater stone: get the sweetwater AS10 http://www.aquaticeco.com/index.cfm/.../9751/cid/2328 For the Hagen Ladder: www.drsfostersmith.com Bottle 2L soda bottles are not balanced and will knock over b/c they are not flat bottomed. Juice bottles' caps have never leaked from the threads in my experience. (if they do drink more juice and get yourself another bottle). If you are really worried about the bottle knocking over, purchase a small bucket and place it in there, so there's a barrier surrounding it. Check Valve Prevention System + Yeast Strainer In order to keep the Yeast Muck from being released into your tank, A bubble counter is used to catch the muck. This DIY bubble counter also provides a check valve system to prevent water from back siphoning out of the aquarium. Go to Rite Aid or Longs Drugs and pick yourself up a syringe and find a check valve at your fish store. Take the plunger off, add some glue to the check valve, insert it where the plunger used to be. Fill the syringe halfway with water. The tubing will fit on the end of the check valve, and at the end of the syringe nozzle. Insert this between the diffuser method and your reaction bottle. Congratulations, you've made yourself a bubble counter and a check valve system for your DIY CO2. (picture from a member on another forum). Some plastic check valves occasionally don't work, always check your valve when replacing the DIY CO2 mixture. CO2 will degrade plastic valves over time, so always check. For Larger Tanks For larger tanks, and those that need to lower the ph more, and need more CO2. Using multiple diffusers placed at each side of the tank (left, right, middle, etc) will increase CO2 dissolution. When using the hagen ladder, you can add a T-valve to connect multiple bottles and the ladder, thereby producing more on the ladder. Placing the diffusers under a current will blow the CO2 around and further increase CO2 dissolution and contact time with the water. Is it working? You should see bubbles coming out within 4-24 hours. To see if your CO2 is being properly dissolved based on whichever diffusing method you chose, test your Ph before adding CO2, and after adding. You will see a drop. Refer to a PH and KH chart to see what your levels are at in ppm. http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm This reaction will last at least 2 weeks to 4 weeks. The more yeast added the faster the reaction but shorter duration. Be careful, don't knock over the bottle, and enjoy your CO2. -John N.