Originally Posted by jjp2
you should not get too much more than 10 ppm running a DIY (maybe a 2.5 gallon with 2-3 2-liter bottles right after filling all bottles could be an exception). If you do, there are many on here that would love to know the secret.
You will not have much pressure build up so the powerhead is likely the best option to diffuse.
You should not have to worry about out-gassing at night as you will not have much ppm in the water to start with.
I ran two 2liter bottles of DIY CO2 in my 29 gallon tank for several months, and with the right mixture, could turn a drop checker green all day. 10 ppm is an arbitrary useless estimation at best. There is no reason to be afraid to achieve 30 ppm, unless you are killing fish (you won't). The amount of CO2 produced depends on how much yeast is active in the bottles, and two 2 liter bottles should be sufficient, I would recommend changing the mixture of each bottle alternating every week (so each mixture lasts two weeks only). This will provide steady consistent levels of carbon, and provide good clean growth, as long as you don't overdo it on light. Good luck, and research the info on what you are told in forums