Common in aquaponics: the rules of thumb. For example for the ratio of fish stock to the amount of plants or for the need for fish food. But what are the connections behind it? Due to the cycle with the many players, the processes are complex and not easy to calculate. The rules of thumb are based on estimated values. But if you want to calculate the exact nutrient uptake of plants, for example, you also need to know how evapotranspiration is calculated. It is the "engine" for nutrient uptake. Since we, like engineers, only want to build on hard facts, but many relationships have not yet been fully explored, we have engaged in research ourselves and are now happy to have taken this path. So we are now at the source of current knowledge about aquaponics.