Every plant, including water plants uses light energy to convert water (H₂O) and carbon dioxide (CO₂) to some kind of chemical energy like glucose - this process is called Photosynthesis.

In a planted tank CO₂ is often added to allow for a faster growth and happier plants.
The CO₂ system typically includes the following parts:

• CO₂ Source - provides a way to generate CO₂.
• Bubble Counter - provides a way to monitor the amount of CO₂ added.
• Diffuser/Reactor - provides a way to dissolve the CO₂ in the aquarium water.
• pH Controller - sometimes used for a better control over the amount of CO₂ added.

Pearling - often the result of CO₂ injection