  In closed hydroponic systems, periodic readjustment of nutrient solution is
necessary to continuously provide stable environment to plant roots because the
interaction between plant and nutrient solution changes the rate of ions in it.
The traditional method is to repeat supplying small amount of premade
concentrated nutrient solution, measuring total electric conductivity and pH of
the tank only. As it cannot control the collapse of ion rates, recent
researches try to measure the concentration of individual components to provide
insufficient ions only. However, those approaches use titrationlike heuristic
approaches, which repeat adding small amount of components and measuring ion
density a lot of times for a single control input. Both traditional and recent
methods are not only time-consuming, but also cannot predict chemical reactions
related with control inputs because the nutrient solution is a nonlinear
complex system, including many precipitation reactions and complicated
interactions. We present a continuous network model of the nutrient solution
system, whose reactions are described as differential equations. The model
predicts molar concentration of each chemical components and total dissolved
solids with low error. This model also can calculate the amount of chemical
compounds needed to produce a desired nutrient solution, by reverse calculation
from dissolved ion concentrations.
