Analysis of Water Hardness in Lapindo Mud Sources: Identification of Ca²⁺ and Mg²⁺ using the EDTA Method as a Science Learning Medium. JPSE [Internet]. 2025 Nov. 25 [cited 2026 Jul. 28];1(1):52-9. Available from: https://journal.kopialinea.com/index.php/JPSE/article/view/12