I would think ascorbic acid vitamin C is pretty cheap. I got my bottle of vit c in powder form at Trader Joe's. Cheaper than vinegar. I tried ascorbic acid and got particulate matter precipitating out. I was using organic nutes (my own design). Now, I'm using GH lucas formula for hydro and plants are much happier. I might try it again if CO2 does not work. I'm just tired of lugging gallons of vinegar home to make natural CO2.

Now one guy wants to put a guinea pig in with his grow to generate CO2. That's great! I love all this spontaneous ingenuity.