Do Aquarium Plants Need CO₂? Low-Tech vs High-Tech Explained
CO₂ can transform a planted tank, but plenty of beautiful tanks run without it. Here’s how to decide which way to go.
Plants build themselves out of carbon, and underwater most of it comes from dissolved CO₂. Tank water only holds a little naturally, so carbon is often what limits growth. Injecting CO₂ removes that limit. Whether you need it depends on the plants you want and how bright your light is.
Why CO₂ matters
On land, plants have unlimited carbon in the air. Underwater, CO₂ is scarce and moves slowly, so plants can run short even when light and nutrients are good. When that happens, growth stalls and algae, which copes better with low CO₂, gets the upper hand.
Adding CO₂ lets plants use more of your light. The result is faster, more compact growth, stronger colours and plants that outcompete algae.
Plants that grow fine without CO₂
Many popular plants are perfectly happy in low-tech tanks:
- Anubias, java fern and Bucephalandra
- Cryptocorynes and Amazon swords
- Mosses and Subwassertang
- Floating plants such as water lettuce and frogbit
- Easy stem plants such as Ludwigia repens and hygrophila
See our list of easy aquarium plants for beginners.
Plants that really want CO₂
Carpeting plants such as glosso and Monte Carlo, many red stem plants and delicate species such as Rotala macrandra struggle without it. They tend to grow leggy, lose colour or melt back.
| Low-tech | High-tech | |
|---|---|---|
| Light | Low to medium | Medium to high |
| CO₂ | None or liquid carbon | Injected, steady |
| Growth | Slow and steady | Fast |
| Plant food | Half dose | Full dose or more |
| Maintenance | Light trimming | Frequent trimming |
| Algae risk if unbalanced | Lower | Higher |
How to run CO₂ well
- Use a drop checker and aim for a lime-green colour
- Switch CO₂ on one to two hours before the lights so levels are ready
- Turn it off an hour before lights out
- Increase slowly and watch your livestock. Fish gasping at the surface means too much
- Keep surface ripple steady, because changes in surface movement change CO₂ levels
Unstable CO₂ causes more problems than none at all. Swings can lead to curling leaves and algae.
Match your plant food to your carbon
More CO₂ means faster growth and faster nutrient use, so high-tech tanks need more plant food. Low-tech tanks need less. With PPS-Pro, start low-tech tanks at half dose, 0.5ml per 10 litres of each bottle daily. Start CO₂ tanks at the full 1ml per 10 litres and increase if plants show signs of hunger. Our dosing guide has the details.
Shrimp are sensitive to CO₂ swings and low oxygen. Increase CO₂ slowly, keep some surface movement, and many shrimp keepers simply choose low-tech plants instead.
Quick answers
Do aquarium plants need CO₂ to survive?
No. Many plants grow well without added CO₂. Injected CO₂ mainly helps fast-growing, red and carpeting plants.
Is liquid carbon as good as CO₂ injection?
It helps a little in low-tech tanks but is weaker than injected CO₂. Dose it carefully, especially with shrimp.
Do I need more fertiliser with CO₂?
Yes. Plants grow faster with CO₂, so they use nutrients faster and usually need a fuller dose.
When should CO₂ be turned on?
One to two hours before the lights, and off around an hour before lights out.
Products mentioned in this guide
Everything to start dosing on day one: pre-measured macro and micro compounds, two 500ml bottles, two dosing syringes and a full dosing guide.
Easiest startBoth bottles already mixed for you. Shake, measure 1ml per 10 litres and dose. No scales, no spoons.
Nitrogen + potassiumThe main source of nitrogen and potassium in your macro bottle. Usually the first compound to run low.
Copper-free aquarium plant food.
Dose on day one.
Pre-measured compounds, bottles, syringes and a full dosing guide. Shrimp safe, made in the UK, free UK delivery on every order.
Everything you need to get the most from your planted aquarium.
