i am running 4 diy 2liter bottles on my 125gal long and i have roughly 15-20 or more ppm of co2 in my tank i have found that if you use 2 cups of sugar the water turns into alchohol before the sugar is gone and then even if you up the amount of yeast you end up dropping the length the bottle can run. i do 1 cup sugar to 1/4 tsp yeast and a small amount of baking soda per 2 liter. if i switch all 4 bottles out at once i get well over 50+ppm for about 5ish days. so i only switch out 2 of them per week. as far as i know it does not matter about what kind of water i have used distilled, well, city, lake and stream water and no difference. this is yeast we're talking about the take a beating when you make bread with it so i really don't think you need to be gentle. warmer water makes the yeast activate quicker but too hot kills. too cold and it takes forever to activate.