Diagnosis
Yeah, this one's common. The filters are clogged with mineral scale or fine sediment. The Black Berkey elements have a huge surface area, but they're not magic—they need cleaning.
How to Fix It
You need to scrub the filters. Take them out and use a Scotch-Brite pad (the green scrubby side) or a stiff brush. Scrub the entire outer surface of the ceramic shells vigorously under running water until you see the grayish-white base material come through. This removes the clogged pore layer. Rinse thoroughly.
If That Didn't Work
If scrubbing doesn't restore flow, the filters might be at the end of their lifespan (they're rated for thousands of gallons, but it depends on your source water). Extremely slow flow after cleaning usually means it's time for replacements.
Heads Up
Never use soap, detergent, or any chemical to clean the filters. You'll contaminate the media. says just a scrub pad and water, and they're right for once.