In this paper, the optimization of the formation of some biodegradable complexes and their modeling are discussed. From this point of view, chelators of micro- and macro elements play a remarkable role. The aim of our paper is the investigation of some complexes and ligands having polyamino-polycarboxilic structure. We have calculated the optimal pH of the formations of these complexes and we have identified the sterical possibilities and difficulties with computer modeling. The study of the complicated equilibrum conditions required the prior determination of the stability constants of the metal aqua/hidroxo complexes and the protonation constants of the ligands as well. Excellent linear colleration have been found between the results of our investigation and the data known from the literature. Conclusions: one can gain time and expenses by this easy way of determination of the optimal pH by mathematical calculation. Applying these models we can forsee the process and results of reactions unstudied experimentally before.