Healthy plant growth is based on the following three main pillars: A supply of light, a supply of CO2 and an adequate and optimal supply of mineral nutrients. The supply of nutrients is described by Liebigs Law of the Minimum. According to this concept, the nutrient which is available in the minimum amount limits the growth of plants regardless of whether it is a microelement or a macroelement. Microelements are trace elements which plants need in small amounts, whereas macroelements are used for growth in larger amounts. In a well-planted aquarium, both microelements and macroelements are consumed in large amounts. Particularly when the fish population is small, the microelements, as well as the macroelements of nitrogen, phosphorous and potassium, quickly drop down to the minimum.Potassium plays an essential role in all vital functions. In plants, for example, potassium is directly involved in stomatal regulation. In addition, potassium carries out important functions in the regulat