I have DIY CO2 on my 45 gallon tank, working very well for a month now. I get about 2 bubbles per second, slowing to about 1 bubble per second at 3 weeks, when I change the solution. My bottle is a 3 liter cranberry juice bottle. I load it with 3 cups of white sugar, one teaspoon of baking soda, and 1 teaspoon of bread machine yeast. I start getting the 2 bbs in about 4 hours after setting it up.
I have a little white, fine pore airstone I run the CO2 into the tank water with, with the stone below the canister filter inlet, so some of the bubbles get sucked into the filter. I like that arrangement because it is so easy to monitor the CO2 production, just by observing the stream of fine bubbles in the tank.
This has helped my plants to grow much faster, and all look very healthy, so I'm convinced everyone who can't afford a pressurized CO2 system should use DIY. I'm using low light, by the way.