Question

source of carbon dioxide for aquatic plants

Answer 1

The main source of carbon for plants is carbon dioxide (CO2). Terrestrial and aquatic plants with emerged or floating leaves usually absorb sufficient amounts of CO2 from the air with their leaves. The average concentration of CO2 in the air is currently 0.039 vol%.

Answer 2

Plants require carbon dioxide to create their own foods (photosynthesis). They obtain carbon from either carbon dioxide (CO2) or some plants take it from calcium hardness (KH).
It is easier to for plants to utilise carbon from CO2, which is naturally present in aquarium, but not usually at the levels required. As CO2 levels disapper, plants slow their growth, forcing them to use carbon from KH, which is the ingredient that holds pH stable.When this bufferes content is low, pH level can change dramitically, which may severly stress or even lead to the death of the fishes.

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