Admittedly, even without CO2 fertilisation, some aquarists say they observe their plants growing. There are several reasons for this. One is that the needs of our aquarium plants differ as much as those of our fish (discus/goldfish). Some plants, such as the Vallisneria, need very little fertiliser, only a little light and can survive with the CO2 content of untreated water. Any high maintenance plants, such as Rotala macranda, would perish miserably if forced to share an aquarium in these conditions. But the Vallisneria too would flourish still further, were it to receive CO2 fertilisation, assuming there is enough fertiliser and light.
The correct CO2 content in the aquarium
CO2 is dissolved in ALL water, as it diffuses from our air into the water. Unfortunately, that’s not enough for most aquarium plants. In the following table you can read how much CO2 is dissolved in your aquarium water at a certain pH value and a carbonate hardness X. The ideal CO2 content is marked in green. This makes it easy to see how much CO2 is still missing in your aquarium water so that your plants get enough nourishment.
If, let’s say, your pH is 7.4 and the KH is 6 °dKH, then you have 7 mg/l CO2 in the water. However, most aquatic plants need somewhat higher CO2 levels, of between 14 and 23 mg/l, to grow vigorously and healthily. Very sensitive species can even need 23 to 36 mg/l. With the help of a CO2 fertiliser system you can increase the CO2 content in the water and at the same time set the perfect pH value for your fish.
Find more about CO2 plant fertilisation here: CO₂ plantenbemesting