Small particles of carbon called carbon "fines" are normal to be present in a new GAC filter when it is first installed. Carbon "fines" appear in water as a suspended solid that is black or gray in color. They are generally only noticeable when new filters are first installed. They are also generally found more in GAC (Granular Activated Carbon) carbon filters. All filters should be generously flushed with several gallons of water before used for drinking. Especially GAC filters should be generously flushed to wash away the carbon fines. This will wash away the carbon fines and make the filter ready for use.