Is my cartridge clooged with mineral deposits?

After thoroughly cleaning the cartridge with a degreasing agent, flush the cartridge with a garden hose to remove all traces of soap, etc. Now apply several drops of acid directly to a small area of the filter media. If bubbling occurs, this indicates a build-up of calcium or minerals, and you should proceed with a mild acid soak. If no bubbling is observed, your cartridge most likely does not require acid washing.