In addition to CO2 and light, aquarium plants require nutrients in the substrate and the water for lush and healthy growth. The two basic categories of essential plant nutrients are macro and micro-nutrients. Macronutrients consist primarily of nitrogen,phosphorus, and potassium, while micronutrients include calcium, chloride, iron, magnesium, manganese, sulfur, zinc, and other trace elements.
Without supplementation, plants are unable to thrive since natural concentration of nutrients such as potassium is relatively low. The nutrients need to be replenished routinely to maintain adequate levels, especially micronutrients, since many of them are utilized quickly and do not remain available for more than a few days.