This work aims to evaluate its effect on cell density, biomass, and proximal composition in semicontinuous cultures. Thalassiosira weissflogii was cultivated in five culture media, for which the f medium was taken as reference, and the concentrations of nitrates, phosphates, and silicates were modified up to a factor of four in five treatments (f/4, f/2, f, 2f, and 4f). Cell density and biomass increased as the initial nutrients rose in the treatments. Protein and lipids (mg L-1) in the biomass of T. weissflogii were higher in the 2f and 4f treatments for the three partial harvests. The lipid biomass in the cultures was higher than with proteins and carbohydrates for all treatments, with 2f and 4f being the most concentrated. The concentration of nitrates, phosphates, and silicates of the culture media, declined as the cell density increased in all cultures, decreasing more than 90% in phosphates and 94-98% for the silicates for the initial concentrations. At the cell level, the percentage of carbohydrates related to dry weight in T. weissflogii increased as the level of the f treatment decreased. Meanwhile, the protein fraction declined when the level of the f medium was either increased or decreased. The data reported in this study can be useful for producing T. weissflogii in a 30% semicontinuous system, obtaining more controlled biomass production per day with an estimated value of its proximal composition, based on the level of the f medium.