I run three 64oz juice bottles into a 12oz Gatorade drip/snot bottle, then into the intake of my fluval fx5 on my 125. It's not much, and I just upgraded from one to three bottles about a week or two ago, not enough time to tell a difference yet.
In a 1-liter bottle: half- to two-thirds full with warm water, add 1/2 cup of sugar and 1/2 tsp of yeast. It's just that simple. Lasts about 2 weeks. Start a bottle, then a week later start another, a week after that replace the first bottle, etc.
2 liter bottle I used 2 1/2 cups sugar filled to the brim, 1/4 tsp yeast & one energy pill. Don't ask why i figured it wouldn't hurt to throw something random as i was running two bottles. I got a little over 3 weeks