i was watching my tank after i cleaned it and something started to move. it was as if the rock came alive. This thing moved over 3 rocks. It is 3 inches big!! i think its a crab of some kind, except its hairy...ahhhh
Put a small glass in the tank with some food in it next to a rock... the "crab" will climb inside and won't be able to get out. Then you can take some pictures and show us so that someone can make an ID for you.
Andy is right... most "hairy" crabs are no good... lets see if you can catch him so we can figure out what he is!