Just so happens that I started up my first jello mix, today. I use DIY for 2.5-gallon and 5.5-gallon tanks.
Here is the recipe I'm working with:
1/2 packet of Knox gelatin
1/2 cup boiling water
1/2 cup sugar
pinch of baking soda
Mix the above ingredients until everything is dissolved.
Add 2 or 3 ice cubes to cool the solution and pour into small plastic soda bottle (~590 mL?).
Refrigerate until set.
Dissolve pinch of baker's yeast (~1/16 tsp) and pinch of sugar in small amt of water and add to bottle.
Fill with more water up to "shoulder" of bottle (3" below mouth).
I'm giving it a day or two to get started before I replace the old mixes with these. Hopefully, these will last longer and run more steadily. Even my non-jello mix lasted a good 5-6 weeks. Just be careful not to go heavy on the yeast.
If this post is still active in a week, maybe I'll give an update on how the jello mix is working out.