Bad Day at Black Rock-----

great movie,

probably bad aquarium situation. Even with the Bio-Spira, my ammonia level
spiked up, so I did the ol` water change.
While siphoning I knocked into a rock, and it crumbled revealing
black-as-tar innards. This stuff looks real bad. It reminds me of the black
ash remnants left after a camp-fire.

Is this a normal thing? Any special actions to take?

thanks