I recently bought some more LR, and I was just re arranging it (putting some LR rubble into a filter is good, right?) and I picked up the LR and noticed a lot of little worm things. They looked like they moved with their legs, maybe almost like little shrimps or something. What could these be? Also, there were holes on parts of the LR, and they seemed to be surrounded by a very fine looking sand, almost a muck type of substance, what would this be?