In nature, CO2 (carbon dioxide) is a primary nutrient for almost all plant organisms. This applies to plants growing on land, but certainly also to aquatic plants. Under the influence of (sun) light, plants absorb CO2 and convert it into sugars, which are needed for growth. CO2 is therefore a very important factor in the development of pond plants.The contents of the package are sufficient to treat 4000 litres of pond water with CO2.The CO2 Tabs from Velda provide this necessary CO2. Just add the tablets to the water and they already effervesce CO2.