Do It Yourself Carbon Dioxide Injection

For those of you who have thought of using carbon dioxide (CO2) injection in your planted aquariums but have been put off by either the cost of available systems or have been unsure what the effects of CO2 injection on plant growth may be, then this article describes an inexpensive and easy to assemble DIY system that uses yeast to produce the CO2. The CO2 injection system consists of a generator which holds the yeast mixture and hardware installation which ensures the CO2 is efficiently dissolved in the aquarium.

Hardware contains:
- 2 litre plastic soft-drink bottle;
- airline tubing;
- bubble counter;
- valve;
- reactor CO2.

The CO2 generator is simply made from a 2 litre plastic soft-drink bottle, remove the lid, attach a siphon head and block it to stay open all the time with a toothpick. If you don’t find one, then drill a hole through the lid, force some airline tubing through the hole and seal both sides with silicone sealant. Ensure that this seal is airtight.



Connect the siphon head with the airline tubing. At the other side you connect the bubble counter, which you can buy it or improvise it.



After the airline tubing attach to the bubble counter you attach a valve, so the water from the aquarium not to drain in the 2 litre bottle. At the end of the installation is the reactor of CO2. The purpose of a reactor is to aid in dissolving the CO2 in the aquarium water.



The final step is to prepare the mixture which will produce the CO2. The recipe I use generate 1 bubble /sec. If you want more or less just increase / decrease yeast quantity.
What you need for 2 litre bottle:
- 5.5 water cups;
- 1.5 sugar cups;
- 20g gelatine;
- 0.5 teaspoon yeast;
- 1 teaspoon sodium bicarbonate.

Preparation. In ½ could water cup dissolve the gelatine and let it for 5 minutes. In a pot place 2.5 hot water cups and dissolve the sugar. Add the gelatine in the pot. Put the pot on stove and often mix. When the mixture get warm, remove the pot from the stove. It’s not good to boil because gelatine is destroyed. Add sodium bicarbonate and mix it well. Allow to cool until it can be poured into the bottle. Put the bottle in the fridge and let it for a few hours until the mixture become densely. After that take the bottle from the fridge, add 2.5 warmly water cups in which the yeast was dissolved. Connect the bottle to CO2 installation and in a few hours will start production of CO2.

In order to maximize the benefit of injecting CO2 it is important that you reduce any surface turbulence as this will quickly allow dissolved CO2 to escape into the air. The best ways to achieve this are to, turn of any aerators, lower any spray bars below the water line, direct the current to run around the sides of the aquarium rather than from top to bottom and/or if you have air driven under gravel filters extend the uplift tubes above the surface of the water. Optimally growing plants will produce more O2 and saturate the water with O2 better than any other method you can try.

An increased CO2 concentration will not displace dissolved oxygen (O2) from the water. It seems to be generally accepted that a concentration of 15-20 parts per million (ppm) is ideal for optimal plant growth and that CO2 concentration must exceed 30ppm before becoming dangerous to fish (although the pH drop caused by suddenly injecting this amount probably will).

The yeast system described requires some care and maintenance, but is an excellent and inexpensive way to experiment with CO2 injection. May your plants live long and prosper.