Replacement or upgrade for 4.5-inch x 20-inch systems Bone Char Carbon filter Radial Flow Carbon filter Standard 4.5-inch x 20-inch filters Replacement filters. Bone char carbon is typically used to reduce fluoride, arsenic, radioactive isotopes, iron, lead, mercury, aluminum, silver, bromine, manganese, chemicals, tastes & odors, chlorine, chloramines, herbicides, pesticides, MTBE, and THM. The radial flow carbon offers 20-micron sediment filteration as well as additional carbon filtration with lower flow restirction than typical carbon block filters.