DIY: CO2 for Plants

CO2 is an essential ingredient in plant growth and for aquatics. This presents a special challenge because aquatic plants must rely on what is present in the water. High-tech CO2 systems are expensive and difficult to set up and maintain. A simple DIY CO2 generator is an inexpensive way to supplement CO2 in small aquariums and to gain experience before moving on to a high-pressure setup.

  1. CO2 Generator

    • A CO2 generator can be any airtight container capable of holding liquid, with a removable top for cleaning. A plastic two-liter soda bottle is often used. Install a valve at the top of the container to attach the air tubing. Obtain valves at a hardware store or in pet stores that sell air pump systems. Drill a hole in the bottle cap and seal the valve in with silicone sealant like what is used to fix leaking aquariums. If you use T valves, multiple bottles can be chained together to increase CO2 production capacity.

      Yeast cells release CO2 as a natural byproduct of consuming sugar. The yeast solution consists of yeast, sugar, water and baking soda. Use regular baking yeast or specialty yeasts from home brewing stores. Champagne yeast is used by some people because it can take a more acidic environment, which lasts longer in the bottle. Sugar is the food for the yeast, and baking soda raises the pH of the solution to neutralize the acidic side effect of CO2 production.

      Include a check valve in-line somewhere between the tank water and the generator. This blocks air from flowing backwards into the CO2 generator, which keeps the tank water from siphoning out.

    CO2 Reactor

    • The yeast mixture produces CO2 bubbles slowly, one every few seconds depending on the capacity of the generator, and they will need to be dissolved into the water using a reactor. Keep the CO2 in contact with the water for as long as possible or until the bubble is completely dissolved. The smaller the bubble, the easier this is for you to do. The simplest method is to use a bell, or an upside-down cup or jar that holds a bubble of CO2 under the water. If you have a high-quality canister filter, the bubbles can be directed into the intake tube, where they will be broken up and dissolved by the impeller.

      You can also use fine-bubble airstones, ceramic disc bubblers or bubble ladders as reactors. Redirecting the bubbles into the venturi or intake of a powerhead, or any pump that keeps the water moving, allowa the CO2 to stay in contact with the water for as long as possible.