Nutrient solutions can be considered as aqueous solutions of inorganic ions. The pH of a nutrient solution is a property that is inherent to its composition. If another pH is aimed at, this can only be reached by changing the elemental composition. The pH of an aqueous solution is determined by the initial concentration of acids and bases. In the case of nutrient solutions, this is dihydrogen phosphate (H2PO4-), bicarbonate (HCO3-) and/or ammonium (NH4+). In this study, formulas are derived to calculate the pH of a nutrient solution as a function of the concentration of H2PO4-, NH4+, and/or HCO3-. The pH of a nutrient solution affects the dissociation, complexation, and precipitation reactions occurring in nutrient solutions. These chemical reactions significantly impact elemental speciation and bioavailability, and therefore, have to be taken into account in hydroponic plant nutritional research. The term ''speciation'' indicates the distribution of elements among their various chemical and physical forms like: free ions, soluble complexes, chelates, ion pairs, solid and gaseous phases, and different oxidation states, all of which influences their reactivity, mobility and bioavailability. A good knowledge of the chemical reactions occurring in nutrient solutions is the first prerequisite in hydroponic plant nutritional research. The pH of a nutrient solution is determined by its initial concentration of H2PO4-, NH4+, and HCO3-.
