a dead crab would cause bad water quality if left in there too long and yes the bad hair and slime could be caused from overfeeding, well the slime anyway its a buildup of bacteria, and a good clean up crew would help control the hair algae...are you using tap water?...and ur gonna probably get some responses to take out the biobale..is it a bak pak?..and whats the flow like in the tank?..hth