Crab I.D.

I have a bad long hair algae problem but it is brown instead of green...it doesnt seem to be spreading to quickly though...I got some crab's called Algae eating crabs? Thats what the sign said...One of them is rather large and his conch type shell is about and inch and a half long and about a half of an inch tall...his legs with the claws are sorta hairy and has a white stripe down the edge with red spots on them...any Idea what type of crab this guy is...he is only out at night the others are out in the day...they have black legs with the claws and white spots. Any idea what they are....two id's would be great....is the big one going to gwt out of hand when he gets bigger?
Danny

 

Sounds like hermit crabs. Any chance of some photos?

Chuck

 

pics plz?