DIAGNOSIS The black specks are granular activated carbon fines from inside the Black Berkey filters. This indicates filter media is escaping, often due to a damaged filter element.
FIX Step 1: Immediately stop using the system. Step 2: Disassemble and remove the filters. Step 3: Inspect each filter closely for cracks, especially around the bottom dome or the stem. Step 4: Submerge a suspect filter in water and squeeze it gently. A stream of bubbles from a crack confirms failure. Step 5: Replace any cracked filters.
IF THAT DIDN'T WORK If filters are intact, the specks may be old carbon dust dislodged during moving. Flush the system with two complete chambers of water, discarding the output.
HEADS UP Do not consume water with black specks. A cracked filter shell compromises filtration and requires replacement. The filter warranty may cover this.