I'll give you a brief synopsis of my experience with the DIY CO2 method. First off, you should know that adding more sugar will make the CO2 bubbling last longer, although it will be at a somewhat slower pace. On the other hand, adding more yeast will cause it to bubble faster, killing off the yeast faster as well. If you aren't seeing any bubbles yet and you're sure you mixed it properly, shake the bottle a bit, but be careful you don't to it too much. Shaking it a little can help speed up the reaction, but if you do it too much, you can get some yeast leech its way into the tank, which will make a complete mess (this happened to me, so just a warning). If you take it easy with the shaking, you should be ok. I always used tap water(which is very hard and high ph, so it will work with tap water). I simply found the DIY method to not last very long(maybe 2 weeks if you're lucky, than you'll have to remix another batch. Having said that, I decided that it was more trouble than I was willing to deal with and I ended up buying a CO2 cannister, regulater and the whole bit. A bit more expensive -- maybe $30-40 inititally for the bottle, plus ~$50 for the equipment, maybe a tad more. Once you have the bottle, you can take it to any welding supply store or beverage supply and have it refilled for ~$20. I did that today as a matter of fact, but the just exchanged my empty for a full one and charged $23 -- maybe a tad high, but still not bad, considering they last 2-3 months. Anyway, good luck to you, and again, I highly suggest shaking the mixture a bit until you see it bubbling, just don't do it too much. Cheers,
-Ryan