practice
Planted tank with CO₂ vs without
Do you need CO₂ injection for a planted tank?
Short answer
No — but the plant list changes. Without CO₂, choose slow undemanding species and keep the light modest. Most persistent algae problems come from running high light without the carbon to use it.
Side by side
| Dimension | With CO₂ injection | Low-tech, no CO₂ | Favours |
|---|---|---|---|
| Plant range | Almost anything | Anubias, ferns, mosses, crypts, Vallisneria, hardy stems | With CO₂ injection |
| Growth rate | Fast | Slow | With CO₂ injection |
| Trimming workload | Weekly | Occasional | Low-tech, no CO₂ |
| Algae risk | Low if stable, high if CO₂ fluctuates | Low if light is modest | Neither |
| Equipment cost | Substantial | None | Low-tech, no CO₂ |
| Risk to fish | Real if overdosed | None | Low-tech, no CO₂ |
| Carpet plants | Achievable | Only the easiest, slowly | With CO₂ injection |
Which to choose
With CO₂ injection
Add CO₂ if you want carpeting plants, red stems or fast growth, and you will maintain it consistently.
Low-tech, no CO₂
Stay low-tech and match the plant list to the light. This is the more reliable path to a tank that looks good in a year.
One caveat
The failure mode is asymmetric. A low-tech tank with too much light grows algae; a high-tech tank with interrupted CO₂ grows black brush algae and can suffocate fish. Consistency matters more than the choice.