Will Anthracite Coal from a Multimedia Bed Block Cartridge Filters?

Very high differential pressure increase was detected across cartridge filters (1micron size). Differential pressure went from 10 kpa to 30-35kpa in the space of a week. By taking off the cartridge filters, was noticed anthracite coal on the surface of the filter. Also SDIs were taken before (6.9) and after the multimedia filtration (4.9). SDIs are really high too and we have never seen anything like that before. Asking for opinions and hopefully from experience. What will be my first root cause for the blockage, the anthracite coal or the high SDIs? Thank you!