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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 often use pressurized CO2 gas in high tech planted tanks to boost the speed of plant growth, but what if you don’t want to mess with an expensive CO2 injection system? Many companies claim that liquid CO2 is a good substitute for CO2 gas, while others maintain that it is actually a chemical treatment for getting rid of algae. Keep reading as we discuss what is liquid carbon and how to best use it in your planted aquarium.

What is Liquid Carbon?

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 may see it sold in the United States under brand names like Seachem Flourish Excel, API CO2 Booster, and our own Aquarium Co-Op Easy Carbon. Almost all of these products contain glutaraldehyde or similar chemicals, which is known to reduce algae growth within a planted aquarium. When there is less algae competing for nutrients, light, and carbon dioxide, aquatic plants often grow faster and healthier as a result.

Does liquid CO2 replace pressurized CO2 gas? While liquid carbon is often marketed as a source of carbon, many planted tank experts agree that it is a poor replacement for CO2 gas. In reality, many aquatic plants prefer to grow with their leaves out of water because it is easier and faster to directly access CO2 from the air. Therefore, people set up high tech tanks to help their underwater plants by injecting more CO2 gas into the water at concentrations ranging from 10-30 ppm. 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, a normal aquarium with good surface agitation and gas exchange using an air stone or filter results in approximately 3-5 ppm CO2 in the water, which is still higher than what liquid carbon appears to supply.

pressurized CO2 injection in planted aquarium

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 is the difference between liquid carbon and activated carbon? While their names may sound similar, liquid carbon is used in planted tanks, whereas activated carbon is used for chemical filtration. Activated carbon is a type of filter media that specifically traps medications, tannins, and other impurities from the water.

Is liquid carbon dangerous to humans? Treat glutaraldehyde as carefully as you would treat bleach. Do not swallow, inhale, or touch the liquid. If you get it on your skin, rinse it off. If you get it in your eyes or mouth, rinse thoroughly for 15 minutes. For USA customers, reference the poison.org website. 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 Liquid CO2 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. Unless the tank is balanced so that plants grow well enough to outcompete algae, the algae will keep coming back, no matter how much Easy Carbon is used. Easy Carbon contains 1.5% glutaraldehyde and 0.5% citric acid, and a 16 oz (500 ml) bottle treats 5,000 gallons of water.


How often should I use liquid carbon? Dosing with Easy Carbon is very simple, since the bottle already comes with a pump head. Dose 1 pump (1 ml) of Easy Carbon per 10 gallons every other day for low light aquariums. Use the same dosage on a daily basis for medium to high light aquariums. When in doubt, start with a lower dosage and increase the dosing after evaluating its effects for two weeks.

Liquid carbon can also be used for spot treatment on stubborn algae like black beard algae. Turn off the filter and circulation pumps, and use a pipette to spray a few leaves underwater with Easy Carbon as a test. After a few minutes, you can turn on the filter again. If the algae has been affected, you should see signs of weakening and discoloration in 4-7 days. If the spot treatment is successful, try targeting a few more leaves the next week. Do not overdose the tank beyond the recommended amount of liquid carbon or else the plants in the aquarium may be adversely 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. If you have sensitive plants like these, consider dosing at half the recommended amount.

planted aquarium with vallisneria

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

Why does my tank get cloudy water after using liquid CO2? Because liquid carbon is killing off algae, little particles of dead algae may detach and float into the water column. 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. Try reducing your daily lighting schedule in 2-hour increments using a power outlet timer, and wait at least 2 weeks to evaluate the results before making another major change.

If your aquarium consistently has very low nitrate levels around 0-5 ppm, your plants may not be getting enough nutrients, so trying dosing some Easy Green all-in-one fertilizer according to the directions. 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.

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