Help! DIY CO2 output low
Well I have recently set up a 20 gal planted tank. I am planning on using the DIY CO2 but I'm haveing a problem with how much it produces. I set up a two liter bottle 3/4 full of water(room temp) dissolved 2 cups of sugar in it, in a seperate little bowl I added some sugar water and 1/2 teaspoon yeast and stirred vigerously to aireate the mixture let stand for 10 mins and then added that and 1 teaspoon baking soda to the two liter bottle, after about 3 hours I started getting bubbles but after two days its only up to about 1 bubble every ten seconds.
I always though that I would be able to get around 1 bps or somerwhere close to that, should i just add another bottle to the system? Please help me with this problem.