Yes, 6 months, typical filter is good for about 200 gallons.6 months seems to be the standard. I cut one open a couple years ago and it was nothing but a chunk of charcoal....I guess it's supposed to absorb all the impurities?
It is composed of VERY fine activated carbon. Which removes cysts and greatly reduces impurities, ex. chemicals such as pesticides, pharmaceuticals, chlorine and other bad stuff.
After 6 months its worthless and if you care about the above, change it.