SR-115: Replace the shower filter every 3-6 months or every 5,000 gallons
http://www.waterfilters.net/culligan/showerfilters/sr-115.htm
The Pentek 158673 KDF filter reduces more contaminants. KDF reduces iron, hydrogen sulfide, heavy metals, and bacteria from water. The SR-115 filter does not have KDF in it.
http://www.waterfilters.net/Pentek-158673-KDF-Shower-Filter_p_0-2278.html
Thank you,
WaterFilters.NET