I always had a problem using colored and flavored Jell-o, it just seemes wrong to me!
You can substitute Knox gelatine and save several bucks.
I use the Knox Blox recipe on the back of the Knox box, substituting water with 2 cups of sugar for the fruit juice in the recipe on the box.
I am now using the Blox, 1/3 of the full recipe, in large blocks to fit into my 2L juice box generator, with 1/4 teaspoon of bread yeast (no baking soda or yeast nutrient that I had been using occasionally). It tends to fillup my power reactor with gas up to 1/2 inch deep, so it may actually overdose small tanks. 1/4 recipe might be better, in fact, as it does foam some, didn't do that when I used 1/4 of the Blox.
Anyhow, 1/4 of the Blox will last 3+ weeks, so a $1.20 pack of Knox lasts for 12 weeks. 1/3 of the Blox still lasts 3 weeks runs faster, stops more suddenly, maybe just under 3 weeks in fact.