I too am interested in creating a DIY CO2 injector for my 29g. and have a few questions. I really do not want to add too much CO2 to the tank as my ph is already kinda low, at around 6.8. My plants never seem to really thrive or survive for that matter, for a long time. I was wondering if anyone who had experience with this has a safe formula i can use to inject a small amount that really will not change water parameters, and my plants will at least stay green and survive. I did add some salt to treat ich recently and my plants are getting worse, so i thought i could build this to help them a little until the salt will get out. Another question is how do you guys refill or change the bottles to keep the CO2 going? Do you just start over with a new bottle, or add all the ingredients again, or just sugar or yeast...... Also does the CO2 have to be taken out at night, or do i leave it in there while the plants aren't photosynthesising?