This is the easiest part of the project, making your mix. While there are hundreds of ways to make this mix it really is up to you. Depending on the amount of bubbles you want and the length of time between changes. If you want longer times between mixture changes then you will want to use less yeast. With using less yeast you will have less bubbles. The more yeast the more bubbles, but more changing. The reason you have to change the mixture when using more yeast is as the yeast uses the sugar it produces alcohol and this in turn kills the yeast, not to mention that the more yeast the faster it uses the sugar up.
Now I am not going to bore you with all the science behind the usage of CO2, I will say this. I have run my system and never had any problems with my plants or my fish. There are some that say you can put too much CO2 in and others say no. I have no degree in science on this , but I can offer what works for me. From what I have read says that no matter the amount of CO2 the plants will use it and replace it with O2 even at night the balance will be no different than a tank with no CO2.
Lets see the mixture
The first thing you are going to need to do take your yeast and start it in 1/2 cup warm(NOT HOT) tap water. Again its up to you as to how much yeast you use. Personally I use 1 teaspoon of yeast per bottle. I have tried using 1/2 teaspoon but I wasnt real pleased with the results. This is where you get to experiment.
Make sure that you mix it well as seen in the next picture
Set this off to the side and leave while you do the rest of the mixture. Now you are going to want to add 2 cups sugar to the bottle, after adding the sugar you are going to want to add warm water to the top of the soda label as seen here
As you can see in the last picture that the sugar is undissolved in the bottom of the bottle, you can shake it but it wont all disolve which is fine. I just put the sugar in the bottle and fill with water to the line. I have found that enough of the sugar is dissolved to get things going.
Next you are going to add your pre-mixed yeast
After you put the yeast in all thats left to do is put the cap on tight and hook it up
