Tóth, Žigmund, H. Frančáková, M. Solgajová, and Å tefan Dráb. “WATER HARDNESS AS AN IMPORTANT PARAMETER OF PH”. Journal of Microbiology, Biotechnology and Food Sciences, vol. 2, no. special issue 1, Feb. 2013, pp. 2043-51, https://office2.jmbfs.org/index.php/JMBFS/article/view/7301.