AquariaWise is a participant in the Amazon Associates program and a few other affiliate programs and may earn from qualifying purchases at no extra cost to you. However, we have vetted every program in this guide and believe they are the best for generating affiliate revenue. You can read our full affiliate disclosure in our privacy notice.
If you want the plants in your aquarium to be lush and beautiful, and even successfully grow demanding species like red aquatic species, you will often here experts say to dose your tank with CO2.
But does this really work, and is it necessary!
Well, lets find out.
Aquarists add CO2 to the freshwater aquarium to accelerate plant growth. But care should be taken to control how much carbon dioxide is present to prevent ph swings, or in extreme cases, ph crashes.
For the most part, a large percentage of aquarium plants won’t require a CO2 system or even supplementation. However, a little dosing is essential if you want your plants to establish faster.
The general rule of thumb is if you wish to grow plants that are sold as medium or advance in your local aquarium store, you will need to use extra CO2, plus fertilizer and adequate lighting. But most plants marked easy do not require extra carbon dioxide.
Also, note that when surplus CO2 is added into a planted aquarium, it needs to be coupled with enough lighting and fertilization. Using CO2 in isolation will cause ph swings or even crashes in extreme cases.
See more insight below.
How Much CO2 is Needed For A Planted Aquarium
Carbondioxide is the prime source of food for all plants (including those used in aquascapes); they convert it into sugar through photosynthesis. So if there is a shortage of CO2 in your tank, it will inhibit your plant’s growth.
However, too much of it would be detrimental to your plants and fish health, the same way excess light or fertilization is bad.
For a planted tank, you should aim to inject as much CO2 as the most Carbon dioxide sensitive plant that your are currently growing requires, though one downside to this method is knowing the amount different plants need.
As such, I recommend new aquarist to start with easy, undemanding plants such as Java Fern, Hornwort, Amazon sword, and Java Moss.
That said, most aquascape plant species will do well with a C02 level anywhere from 20 to 30 ppm, with the amount also safe for tropical fish commonly kept in home aquariums.
Any CO2 amount above 50ppm will stress your fish and might even kill them if not resolved. The Kh (carbonate hardness), atmospheric CO2, and the amount released by your fish should also be considered when injecting surplus carbon dioxide in your tank.
CO2 is a gas dissolved in the aquarium and makes your water more acidic (like fizzy drinks). When plants have no light for photosynthesis. the carbon dioxide starts to build up and lower the ph.
Do Fish Provide Enough CO2 For Aquarium Plants
Carbon dioxide is produced by fish and bacteria as they breathe, whereas plants and algae consume and remove the CO2 from the water during the day but revert to removing oxygen at night when photosynthesis stops.
Without CO2 supplementation, your plant depends on the amount that dissolves in the water naturally, plus what is released by your fish.
So, depending on the number of animals you have and the species of plants your growing, the amount might or might not be enough.
Essentially, a heavily stocked tank will have more carbon dioxide than in a lightly stocked tank with lesser fish. Meaning it will support a wider variety of aquatic plants, albeit harder to maintain.
CO2 sensitive plants like Dwarf Water Lettuce and moderate to high light species such as Madagascar Lace will more or less need some form of C02 supplementation because they are more demanding. The amount released by your fish will quite often not be enough.
That said, please note that regardless of the species of plants or the number of fishes you have in your tank, any CO2 dosing system needs to be turned off at night when photosynthesis stops.
During this period, your plants and fish will all be taking in oxygen and giving out carbon dioxide, meaning the amount will already be too much.
A heavily planted tank will show a natural ph cycle that is linked to the lighting period in your aquarium and photosynthetic activities. The ph will usually be lowest in the morning and highest in the evening. At night when there is no lighting on the tank, CO2 dosing should be off(Seneye).
How To Grow Aquarium Plants Without CO2
Many aquarium plants can grow well without injected CO2. So having a thriving tank without dosing is definitely achievable by all aquarists.
However, this is not hackable for all plants. It’s more straight forward with easy-low light plants like Java moss, Java fern, and Amazon swords.
A good understanding of what makes aquarium plants thrive is also great if you are to attain success.
The first thing you need to know is the difference between low-tech-low-energy plants and high-tech-high-energy setups.
Essentially, plants marketed as advanced will most likely require brightly lit setups, CO2, fertilizer, and a lot of water movement and changes; those are the species to avoid.
Go for low tech plants that do not require sophisticated lighting, carbon dioxide dosing, and fertilization for best results.
Aquarium plants are divided into easy, medium, and advanced. Choose from the extensive easy range when running a low tech tank without surplus CO2 for a better chance of success.
Standard stock lighting and atmospheric CO2 should be enough for the plants you want to grow without surplus carbon dioxide**, but ensure your aquarium is well aerated to allow a maximum supply of air**.
Adding fertilizer in the water column is advisable as well to help the plants grow lush and thrive. For rooted plants, I recommend planting them with tabs placed in the substrate.
A liquid fertilizer is better for floating species and other non-root feeders. Whereas targeted fertilization is ideal if you realize a distinct deficiency in your plants.
Another thing you want to do is clean your fish tank, including the substrate, less frequently. What this does is leave nutrients from the fish waste, leftover food, and old leaves in the tank for your plants to feed on.
Even so, please note that this means doing frequent water tests rest you poison your aquatic animals with ammonia and nitrites.
Lastly, if you plan on adding large and small plants together, ensure you trim the towering species to allow those growing below access to adequate lighting.
How to Increase CO2 in Your Aquarium Naturally
Carbon dioxide enters your aquarium naturally from the atmosphere, from your fish, and other microbiological processes that occur in a planted tank.
As such, the easiest way to improve the supply is by allowing all these activities to take place uninterrupted.
If done well, there should be about 3 to 5 parts CO2 per gallon of water in your fish tank, enough for low and moderate light aquarium plants to grow.
Ideally, you should allow enough air to get into your tank by creating extra surface water movement. Power filters with a waterfall also go a long way. Plus, clean your fish tank less frequently to allow as much microbiological activity as possible.
In case you do not attain the desired amount in your fish tank, you can cheaply and easily set up a yeast fermentation bottle with a feeding tube hooked in the intake of a powerhead or canister filter for extra carbon dioxide supply.
Happy fish 🦐🐠 keeping.