There is a better ghetto solution.
1 Fill a bowl full of baking soda.
2 Buy a ball valve that fits a 2 liter, or use a baby bottle with a single tiny hole so that when turned upside down drips about once every 10 seconds.
3 Fill bottle with vinegar and suspend above bowl.
When vinegar mixes with baking soda it creates CO2.
It is also very cheap.
You will want to make sure that your CO2 rig is ABOVE your plants, as CO2 is heavier than air.