Fish Tank: 2007

Here is a recipe I found at http://www.plantedtank.net/forums/diy/9916-jello-co2-thread.html

This article serves as a beginner's guide to hobbyists looking to get started with DIY CO2, or making the switch to the Jell-O recipe.

The DIY Yeast method works on a simple principle, similar to wine-making (except we won't be drinking the brew). Yeast are single-celled microorganisms that ferment sugar for energy. The by-products are CO2 gas and alcohol. So, our aim is to get some yeast, give it some sugar and somehow "harvest" the CO2 gas and get it dissolved into the water so that it is available to the plants.

The traditional method has been in use for a long time in planted tanks. If consists of an airtight bottle containing water, sugar and yeast, airline tubing leading into the tank, and a means to get the gas dissolved in the water. While this method serves its purpose, it tends to start off with a burst of high CO2, then quicky tapers off and has to be replaced within 2 weeks. The quest for a steady and long-lasting method has lead to the development of the so-called DIY Jell-O CO2. In this recipe, the sugar is dissolved in the Jell-O, and the yeast is added on top of the Jell-O. It results in a more steady and longer-lasting CO2 production because the yeast only gains access to the sugar gradually, as the Jell-O is broken down. This recipe lasts me about 3 months, although individual results vary.

What you'll need:

2-liter bottle (soda or Gatorade bottles work fine) with cap

airline tubing

some kind of sealant

drill, or a creative way to drill a hole

water

1.5-2 cups sugar

ordinary grocery-store baker's yeast, 1/2 tsp (Like Fleishmann's active dry yeast)

2 6oz packs of Jell-O ( or four 3oz packages )

Preparing the bottle

You will need to get one end of the airline tube through the cap into the bottle. Only an inch or so of the tube should be inside the bottle. Then you have to seal off any space around the opening in the cap using any airtight sealant that will stick. I'm not much of a handy-man, so you're on your own for this. I had a more mechanically-inclined relative do this bit for me. I think he used bathtub sealant and it has held for almost a year now. Some people have had problems with the cap not screwing in tightly enough to be airtight - my Coke bottle was fine. In fact, I have changed bottles and used the same cap on both without leakage problems. So be a little creative, or beg someone for help.

Now let's make Jell-O!

Mix together 2 packs of Jell-O (any flavour - all that's gonna go into your tank is the CO2 either way) and 2 cups boiling water. Mix really well until it's all dissolved.

Add 1.5-2 cups sugar and mix well again.

Add 2 cups cold water and mix AGAIN. Make sure the sugar is dissolved and not just collected at the bottom.

Pour the mixture into the bottle and stick it in the fridge overnight, until it actually turns to Jell-O.

Once the jello has hardened, add one cup room temp/lukewarm water and 1/2 tsp yeast. More yeast will produce more CO2. I would suggest starting with 1/2 tsp. If you find that it's not enough, you can always open the bottle later and put in some more.

I advise to starting with 1/2 tsp yeast, and work your way up from there. (You can also decrease surface agitation a bit to retain more CO2.) You should have a KH (carbonate hardness - if you don't have this test kit, you need it NOW) of at least 3 to avoid sudden pH drops (when carbon dioxide dissolves in water it acts as carbonic acid, lowering the pH and making the water more acidic). The greater the KH, the more your pH will resist changes.

Occasionally (once or twice) the yeast mixture on top will have to be refreshed with some more yeast and water. Just dump out about half the water and add some more water and yeast. I'm not positive but I think the alcohol level in the water gets to high and kills the yeast. You'll notice a slowdown of the mixture if you have a bubble counter and can adjust as necassary.