SIHOMBING, J.; BARUS, A. .; PASARIBU, J. Y.; SIRAIT, I. J. The Effectiveness of Activated Carbon Made from Shallot Skin in Reducing Calcium Levels and Total Hardness in Hard Water: Efektivitas Karbon Aktif Berbahan Kulit Bawang Merah Terhadap Penurunan Kadar Calsium dan Total Hardness pada Air Sadah. Jurnal Rekayasa, Teknologi Proses dan Sains Kimia (REPROKIMIA), [S. l.], v. 4, n. 1, p. 38–43, 2025. DOI: 10.68115/reprokimia.v4i1.230. Disponível em: http://akses.ptki.ac.id/jurnal/index.php/reprokimia/article/view/230. Acesso em: 24 oct. 2026.