Pond weed uses the carbon dioxide which is dissolved in the water it is in. The amount of dissolved carbon dioxide can be varied by adding sodium hydrogen carbonate (carbon dioxide solution) to the water. Many other plants take carbon dioxide from the air.

What is the purpose of pondweed?

Cape pondweed, or water hawthorn (Aponogeton distachyos), of the family Aponogetonaceae, is native to South Africa and is grown as an ornamental in pools and greenhouses. Many species of those families serve as food for waterfowl and as cover for fishes.

How can pondweed produce bubbles faster?

When placed closer to a light source, the rate of bubbling will speed up, and as the pondweed is taken further away, the bubbles will slow down again - an instant and visual indicator of the importance of light intensity in photosynthesis.