How to Make CO2 for an Aquarium

Setting up a homemade CO2 system for your aquarium provides a cost-efficient alternative to expensive steel CO2 tanks and diffusers. Once the simple equipment is assembled and installed, making the actual CO2 is a quick and easy process done once every few weeks, and requires only a few household ingredients to get started.

Things You'll Need

  • 2 liter bottle
  • 3/8" drill bit and drill
  • Aquarium air tube
  • Scissors
  • Air tube suction cups
  • Sugar
  • Active dry yeast
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Instructions

    • 1

      Prepare a reaction chamber for your homemade CO2 by drilling a 3/8-inch hole in the lid of a standard 2 liter plastic soda bottle.

    • 2

      Cut one end of the silicone airline tubing at a 45-degree angle, and pull 1/2 inch of the tube through the hole in the bottle cap, from outside to inside.

    • 3

      Place the bottle in a convenient place beneath the aquarium and cut the free end of the airline tubing just long enough to run from the bottle and up into the aquarium, about 3 inches from the substrate.

    • 4

      Cut a bamboo chopstick in half and insert the tapered end of one half snugly into the airline tube. The chopstick will act as a simple diffuser, breaking CO2 bubbles into a fine spray for better absorption in the water.

    • 5

      Fill the bottle three-quarters full with lukewarm tap water.

    • 6

      Add 2 cups of white sugar to the bottle. Cover the bottle opening firmly with your hand, and shake vigorously to dissolve the sugar.

    • 7

      Mix 1/2 tsp. active dry yeast (available in the baking section at most grocery stores) with a small amount of warm water in a separate cup before carefully pouring into the 2 liter bottle. Shake the bottle once more, and then screw the cap tightly into place.

    • 8

      Put the 2 liter bottle beneath the aquarium, and run the other end of the airline into the aquarium. Secure the air tubing in place with air tube suction cups placed along the back wall of the tank glass.