The activated carbon we use is high density, pelleted, phosphate-free charcoal. The activated carbon removes impurities from the water which can cause unpleasant odors and tastes.
These carbon filters are comprised of two reusable nylon mesh sacks each filled with about 10 grams of high density pelleted, activated carbon containing no phosphates. (See this link to understand how they work.) Each half filter should last about 3 months or more.
This is premium grade carbon which lasts longer and performs better than other types and which actually attracts impurities and absorbs them. As the filter sits beside or on top of the pump the entire volume of water is constantly coming into contact with the filter, which attracts and eliminates the impurities.