Hydro-Logic® PreEvolution Chlorashield reduces iron, sulfur, chlorine, chloramines and heavy metals. The pre-filters double the filter life. Great for city or well water! Bacteriostatic qualities do not allow microbes to breed in filter. #728772 is 20 in x 2.5 in. #741630 is 12 in x 2 in. #741640 is 10 in x 4.5 in.