How to Use Liquid Carbon in Your Planted Aquarium

Carbon dioxide (CO2) is a vital resource that live aquarium plants need to photosynthesize and create energy. Hobbyists use CO2 gas to increase plant growth speed in high-tech planted tanks. But what if you don’t want to deal with expensive CO2 injection systems? While some companies claim liquid CO2 can be used as a substitute for CO2 gas and others believe it to be a chemical treatment that kills algae, there are many other companies that support this claim. Continue reading to learn more about liquid carbon and how it can be best used in your planted aquarium.

What is Liquid Carbon, exactly?

Liquid carbon, also known as liquid carbon dioxide or liquid CO2, is offered by many aquarium companies as part of their plant fertilizer collection. You might find it in the United States as Seachem Flourish excel, API CO2 booster, or our Aquarium Co-Op’s Easy Carbon. Most of these products contain glutaraldehyde and similar chemicals that are known to decrease algae growth in a planted aquarium. The growth of aquatic plants is often faster and healthier when there is less algae competing with nutrients, light, carbon dioxide and other chemicals.

Can liquid CO2 replace pressure-treated CO2 gas? Although liquid carbon is often promoted as a source for carbon, many experts in planted tanks agree that it is not a good replacement for CO2 gas. It is much easier and quicker to get CO2 directly from the air than it is to grow aquatic plants with their leaves out in water. People have set up tanks with high-tech technology to inject more CO2 gas into water. The concentrations can be anywhere from 10-30ppm. Some initial studies have analyzed how much CO2 is released from recommended doses of liquid carbon, and the numbers were significantly lower than pressurized CO2. In fact, an aquarium that has good surface agitation, gas exchange with an air stone, or filter, results in about 3-5 ppm of CO2 in the water. This is much higher than what liquid carbon seems to provide.

Liquid carbon is often sold as a replacement for pressurized CO2 gas, but we find it more useful as an inhibitor of algae growth.

What’s the difference between activated and liquid carbon? Although their names might sound similar, activated carbon is used to chemically filter water. Liquid carbon is used in plant tanks. Activated carbon is a type of filter media that specifically traps medications, tannins, and other impurities from the water.

Is liquid Carbon dangerous to people? Use glutaraldehyde the same way you would bleach. The liquid should not be swallowed, inhaled, or touched. It should be rinsed off any liquid that gets on your skin. You should rinse it thoroughly for 15 minutes if you get it in your eyes, mouth, or throat. Refer to poison.org for USA customers. For Canadian customers, reference dpic.org.

Is liquid CO2 harmful to fish? While we can’t speak for other manufacturers, Easy Carbon is safe for aquarium fish, shrimp, and snails when used as directed.

How to Use LiquidCO2 in Planted Aquariums

Easy Carbon is an algae inhibitor that we use to help us when we’re in the process of balancing the light and nutrient levels in our planted aquariums. No matter how much Easy Carbon is added, the algae will continue to grow in the tank unless it is properly balanced. Easy Carbon is made up of 1.5% glutaraldehyde (500ml) and 0.5% citric acids. It can be used to treat 5,000 gallons.

How often do I need to use liquid carbon? Easy Carbon can be used as a daily supplement. The pump head comes with the bottle. Low light aquariums will need to use one pump of Easy Carbon (1 ml) every other day. Medium to high-light aquariums will require the same daily dosage. When in doubt, start with a lower dosage and increase the dosing after evaluating its effects for two weeks.

Spot treatment of stubborn algae, such as black beard algae, can be done with liquid carbon. To test the Easy Carbon, shut off the circulation pump and filter. After a few minutes, you can turn on the filter again. In 4-7 days, the algae should show signs of discoloration and weakening if it has been affected. If the spot treatment is successful, try targeting a few more leaves the next week. You should not give the aquarium more liquid carbon than is necessary. Otherwise, the aquarium’s plants may be negatively affected.

Which plants are sensitive to liquid carbon? Certain plants, like anacharis and vallisneria, are notorious for melting away in the presence of liquid carbon. You might consider doubling the recommended dose if you have sensitive plants.

While liquid carbon is safe for fish and invertebrates, certain plants like vallisneria may be more sensitive to it.

Why is my water cloudy after I use liquid CO2 to kill algae? Small particles of dead algae can float in the water column from liquid carbon. Regular water changes and improved mechanical and chemical filtration can help remove the particles from the water.

Why isn’t Easy Carbon getting rid of algae? If algae is not going away despite regular usage of Easy Carbon, then most likely the tank is too unbalanced in terms of lighting and/or nutrients. Use a power outlet clock to reduce the amount of lighting you use each day. After that, wait at least 2 weeks for results.

Your aquarium may have low levels of nitrate, which is typically between 0-5ppm. If this happens, you should consider adding Easy Green all-in one fertilizer to your tank according to the instructions. If your aquarium always has above 40 ppm nitrate, you can reduce excess nutrients from the water by doing more frequent water changes, feeding less fish food, or moving some fish out of the tank.

For more information on plant nutrients, read our full article on choosing the right aquarium plant fertilizer for you. Best of luck with your planted tank, and enjoy nature daily.