Make a CO2 Reactor for an Aquarium

Planted aquariums thrive with the addition of CO2. However, store bought CO2 systems can cost upwards of $200. A simpler way is to make it your self. Read the article below to find out how.


  1. Drill a hole in the lid of the 2L bottle. The hole should be just a tiny bit smaller than the plastic aquarium tubing
  2. Cut the end of the plastic tubing at an angle. This will make it easier for you to pull it through the hole
  3. Using needle nose pliers, grab the end of the plastic tubing. Pull the tubing through the hole in the lid until you have about {{safesubst:#invoke:convert|convert}} of tubing on one side of the lid. If the hole is too small, widen it with a slightly larger drill bit.
  4. Seal around the tubing by putting a thick layer of glue around the hole where the tubing comes out.
  5. Cut the tubing about {{safesubst:#invoke:convert|convert}} away from the lid. Place a stopper valve on the tubing and reattach the tubing you just cut off.
  6. Attach an air stone to the air tubing on the outside of the 2L bottle.
  7. Fill the 2L bottle with lukewarm water. Use 6-8 cups so as to fill it no more than 3/4 of the way full.
  8. Place 2 cups of sugar in the bottle, using a funnel to pour it in.
  9. Measure 1/2 a teaspoon of yeast and pour it into the bottle.
  10. Secure the lid on the 2L bottle and shake vigorously for 5-10 seconds.
  11. Place the 2L bottle near the tank. Place the airstone inside the tank under the water level. The airstone should start to bubble in 1-24 hours. Usually it takes about 4-6 hours, but don't give up on it until the full 24 hours.



  • Replace the CO2 mixture as needed, depending on your recipe. If you use the recipe in the instructions, you will need to change the mixture about once every 2 weeks. If you use more yeast, you will have to change the mixture more often.
  • Note that the mixture in the instructions will produce a relatively small amount of CO2 but will last a long time.
  • The recipe for the CO2 mixture can be altered to produce more or less CO2. Adding more sugar will cause the reaction to last longer. Adding more yeast will cause more CO2 to be produced, but the reaction won't last as long


  • Never attempt to block the air tubing in any way, this will cause you to have a ticking CO2 bomb in your room.
  • Never leave the lid off a CO2 reactor, the CO2 could leak out and cause someone to pass out.
  • IMPORTANT!!! Adding too much yeast to the container will cause too much CO2 to be produced and will cause a DRASTIC drop in pH which will kill your fish.

Things You'll Need

  • 2L bottle
  • air tubing
  • an aquarium back flow stopper (usually sold to be used with air pumps)
  • needle nose pliers
  • glue
  • airstone
  • drill and bit
  • sugar
  • water
  • yeast

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