DIY: Aquarium CO2 Injector

CO2 is a necessary and vital ingredient of photosynthesis and your aquarium plant̵7;s health. An injector system generates the CO2 and delivers it to the aquarium where it is dissolved in the water and then used by the plants. Buying a CO2 tank can cost near $100, and then after you purchase all the other parts, a solenoid controller and metering valve your investment is near $300 (prices as of 2010). A do-it-yourself CO2 injection system costs no more than $10 to make.

  1. CO2 Generation

    • The basic way to generate CO2 is to do it in a 2-liter used Coke bottle. You place sugar water and yeast inside the bottle and CO2 is the product. You can connect the bottle to the tank a few different ways. One way is to use a simple 1/4-inch tube and a 1/4-inch hole drilled into the cap. You then apply aquarium sealant to seal the hole. Another method is to use a chemical stopper and 1/4-inch copper tubing which goes through the stopper. For larger tanks you can place bottles in series, connecting the bottles with T-connectors. This allows an uninterrupted CO2 supply to the tank.

    The Recipe

    • There are many variations on the recipe to make the CO2. The basic recipe is 3/4 cup sugar, 6 cups of water and 1 tsp. of bakers yeast. The amount of sugar varies depending on the source, from 3/4 cups all the way to 3 cups, but too much sugar can overload the yeast. The only significant variation on the recipe is the use of champagne yeast which is type of brewers yeast. The advantage to using this would be to extend the CO2 generation from two weeks to a couple of months.

    The Reactor

    • The reactor is where the CO2 is dissolved into the tank water of the aquarium. One method uses an upside-down clear plastic bowl as trap where the CO2 bubbles will leak into the bowl and be held there until they dissolve. Another method has the CO2 being discharged underneath the intake of a canister filter. The CO2 bubbles will then be sucked up the intake and dissolved inside the filter where it is then discharged into the tank. The least desired method is taking the CO2 and using an airstone to distribute the CO2 bubbles into the tank. The problem is if you use a cheap airstone much of your CO2 will escape to the air.