I have a DIY CO2 system currently set up on my heavily planted 60 gal. I rotate 3 bottles typically changing one out about every 2 weeks, meaning my formula is generating CO2 effectively for approximately 5 weeks. In the beginning I added the first bottle. I waited a week and added the second bottle. After my growth increased and my drop checker indicated that additional co2 was required I added the 3rd bottle to the rotation. My formula is...
~1 tsp bakers yeast
2 cups sugar
2 Tsp Molasses
1 tsp baking soda
1/4 cup whey protein
3 drops dechlorinator (sp?)
For a 2 liter bottle, I have used this formula in 2 1 liter bottles on smaller systems with different rotational needs.
Yeast can be activated and produce CO2 both anaerobic and aerobic. We are trying to utilize the anaerobic process. So the less exposure to air the better. What I do is mix everything except the yeast in warm water. To ensure that everything is dissolved. I then add it to the bottle and add cold to Luke warm water to fill to a little below the top of the label. At that time I put the yeast with some Luke water. I squeeze the bottle so that the mixture raises to just below the top. Then I add the yeast water mix quickly screw the cap on the bottle, while it is still squeezed. Clap the tubing exiting the top until it is added to the system. You need to shake the bottle either before or after you connect it to the system, while still squeezed. This will produce a surge of CO2 which will more than expand the bottle.
Diffusing can be effectively achieved by placing the end of the CO2 tubing in a large glass applesauce jar and propping it between the side of the aquarium and the outlet of a power head. You can use a smaller jar if necessary. The jar may have to be angled so that no bubbles escape. I am currently using a ISTA max reactor which I purchased online for $10. I have it on the out going side of my canister right before my spray bar. It works great!
I have aeration on a timer turning on 30 min before the lights go out and turning off 30 mins before they come on. The CO2 runs continuously.
Sorry to be so lengthy, and there are a million ways that are all right. This is just what works for me.