The Fish Guru

CO2 and Your Freshwater Plants: A DIY Guide

Freshwater aquariums are a beautiful addition to any home or office space, and the plants within them play a crucial role in creating a healthy environment for the aquatic animals that call it home. One important factor that affects the growth and health of freshwater plants is carbon dioxide, or CO2.

In this article, we will discuss what CO2 is, which freshwater plants need it, and how to create and measure it in your aquarium.

1) CO2 in the Freshwater Aquarium

What is CO2? Carbon dioxide (CO2) is a colorless, odorless gas that is naturally present in the air we breathe.

This gas is also produced by living organisms, including plants and animals, during the process of respiration. In aquaria, CO2 plays an important role in photosynthesis, which is the process by which plants use light energy to convert CO2 and water into glucose (sugar) and oxygen.

Without CO2, plants cannot carry out this essential process, and their growth and health will be impacted. Do Your Freshwater Plants Need CO2?

While some freshwater plants can survive without added CO2, many species benefit from this gas being present in their water. Demanding plant species such as Rotala spp., Bucephalandra spp., Hemianthus spp., Micranthemum spp., Glossostigma spp., Ludwigia spp., Cryptocoryne spp.

need CO2 supplementation to thrive and remain healthy in a closed aquarium environment. This is because there are often not enough natural CO2 levels in an aquarium to support these plants’ enhanced growth requirements.

When CO2 is not present in sufficient amounts in the water, the plant might experience Algae overgrowth, leading to a discolored and an unhealthy environment.

How to Make a DIY CO2 System for a Freshwater Aquarium

Creating a do-it-yourself (DIY) CO2 system for your freshwater aquarium is an inexpensive way to provide your plants with the vital gas they need. To create a DIY CO2 system, you will need a CO2 reactor, which is a device that diffuses CO2 into the aquarium water to improve its availability.

You then follow the following simple steps:

1. Buy a plastic bottle, which will function as the CO2 generator.

2. Add water and sugar to the bottle, making sure to leave enough space for CO2 gas generation.

3. Seal the bottle and attach the CO2 reactor or diffuser to a silicone tubing.

4. Add a bubble counter if needed.

5. Install the CO2 system in your aquarium.

How to Measure Carbon Dioxide in the Aquarium

To measure CO2 levels in your aquarium, you can use a CO2 indicator kit that can be bought at any pet store. A CO2 indicator kit measures the pH level of your aquarium water, which relates to the Carbonic acid generated by the dissolved CO2 gas.

A pH to KH drop checker tests can also help you determine the correct range of CO2 levels to keep in your aquariums.

2) Demanding Freshwater Plants That Need CO2

List of Demanding Species of Plants

Rotala spp., Bucephalandra spp., Hemianthus spp., Micranthemum spp., Glossostigma spp., Ludwigia spp., Cryptocoryne spp., and other fast-growing species require CO2 supplementation or they may exhibit signs of stunted growth, yellowing leaves, weak and leggy stem development, and other visible deficits. Easiest Aquarium Plants That Don’t Need CO2

For beginners or aquarium hobbyists with low-tech planted aquaria setups, consider choosing low maintenance plants such as Java fern, Anubias, and Vallisneria.

These plants undergo photosynthesis marginally and will do well in setups even with little or no added CO2. Conclusion:

To maintain a healthy and thriving freshwater aquarium with lush plants, making sure to provide the right conditions, such as correct CO2 levels, is essential.

Knowing which plant species need CO2 and how to create and measure it in your aquarium are crucial steps to achieving the best results in your aquascaping endeavors. By following the steps above, you can create a happy, healthy, and thriving aquatic ecosystem for your pets and plants alike.

3) DIY CO2 System Assembly & Considerations

CO2 supplementation is essential for most planted aquariums, particularly when growing more demanding plant species. A DIY CO2 system is a cost-efficient alternative to store-bought equipment, as it offers the benefit of having complete control over the CO2 output.

With careful consideration and assembly, a DIY system can be tailored to fit specific needs and requirements. However, there are also some disadvantages to consider.

Below are some pros and cons of a DIY CO2 system. Pros:

– Cost-efficient compared to professional systems

– Customizable to fit specific aquarium needs

– Greater control over CO2 output

– Ability to make replacements for specific parts


– Can be challenging to set up and calibrate

– Carbon dioxide output can be inconsistent

– Short lifespan of CO2 production (usually 1-2 weeks)

– Risk of contamination from mold and bacteria

Materials Needed for a DIY CO2 System

To assemble a DIY CO2 system, several components are required, including plastic bottles, airline tubing, diffuser, yeast, sugar, gelatine, baking soda, and citric acid. Here are the steps to set up a basic DIY CO2 system:


Find a suitable plastic bottle. The bottle should hold at least 2L of water and have a secure lid.

2. Add 2-3 cups of granulated sugar and half a teaspoon of citric acid to the bottle.

3. Fill the bottle with lukewarm water, leaving about three inches of headspace.

Next, add the yeast mixture:

1. Mix a packet of gelatine with warm water (according to the package instructions).

2. Add the yeast to the gelatine mixture.

3. Wait until the yeast forms a creamy layer on top.

4. Pour the yeast mixture on top of the sugar and water in the plastic bottle, and then attach the airline tubing to the bottle.

5. Place the other end of the airline tubing in a diffuser, and then place the diffuser in the aquarium.

6. Watch the CO2 levels to ensure they are sufficient, and adjust as needed.

How Much Carbon Dioxide Do Your Plants Need? The ideal CO2 range for freshwater planted aquariums is between 20-30 ppm.

This range ensures that plants receive enough CO2 to undergo photosynthesis, and also prevents harm to fish or invertebrates. To measure your CO2 levels, use a reagent test kit and add drops until the color of the aquarium water turns lime green.

4) When to Buy a Professional CO2 System

While a DIY CO2 system is a cost-efficient and customizable alternative to professional systems, there are some limitations. For larger tank sizes, i.e., over 40 gallons, and delicate plant species in need of more extensive CO2 supplementation to thrive, a professional CO2 system is the better option.

Below are some specific considerations to keep in mind when deciding which type of system is best for you. Limitations of a DIY CO2 System:

– Recommended for tanks under 40 gallons in size

– Short CO2 lifespan

– Inconsistent output

– Inability to support oxygenation systems

Ideal Tank Sizes for a DIY CO2 System:

– Tanks under 40 gallons

– Low-tech planted aquarium setups

– Aquariums with cheaper fish species, which are less sensitive to fluctuations in CO2 levels

Final Thoughts and Conclusion:

Carbon dioxide supplementation is crucial for most freshwater planted aquariums, but there are several choices for how to set up that supplementation.

A DIY CO2 system offers cost savings and customizability, but it may not be the ideal choice for larger aquariums with delicate plant species. A professional CO2 system is a better solution for this scenario but is more expensive, less customizable, and harder to replace when essential parts break down.

When choosing the right system, prioritize what is most important to the aquarium’s needs, and adjust accordingly. In conclusion, carbon dioxide supplementation is crucial for most freshwater planted aquariums, and understanding the various types of systems and their requirements is key.

DIY CO2 systems offer cost savings and customizability but has limitations and can be challenging to set up and maintain. Professional CO2 systems are better for larger tanks and more delicate plant species, but they are also more expensive and less customizable.

When choosing which system to use, prioritize the aquarium’s needs and follow best practices for setup and maintenance. With the right CO2 system in place, you can ensure your planted aquarium thrives and provides a beautiful, healthy environment for your aquatic pets.

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