Echo Retro/NHM130 Carbon Block FilterThe Echo Retro Carbon Block Filter (previously named NHM 130 Carbon Block Filter) is one of the two necessary filters for the Echo Retro (previously named NHM 130 Machine). The proprietary Carbon Block Filter removes: Chlorine Chloramines Pharmaceutical drugs Water soluble metals Bacteria Algae Pesticides Other chemicals found in water The Carbon Block Filter lasts 475 gallons and should be replaced every six months.