My 2 Litre DIY system only lasts a few days at best. I just built a couple new bottles, they're air tight, no smell of yeast, look great and work perfectly for the first couple days. After that, it comes to a near crawl for a week and nothing.
My exact recipe/procedure is:
1 Cup White Sugar
1/4 TSP of Bread Machine (Instant) yeast
I mix the yeast in it's own water dish, gently, over the course of 5 minutes.
I put the sugar in, fill it just under halfway with water, shake shake shake, then pour in the yeast mixture and shake some more. After half an hour it produces CO2, after a couple hours it's going strong, after a couple days it's garbage.
Am I missing something here? My tap water is non-chlorinated well water and has 8-10dkH and around 7.4-7.6 pH. I figure I don't need baking soda since it already has some hardness to it. As much as I would love a pressurized system I don't have the $200 to spend on the setup right now, or likely ever for that matter.