The Blue Leg Hermit Crab (Clibanarius tricolor) is a nice addition to any saltwater reef tank because it is extremely good detritus eater and will aid in the removal of excess food, waste and algae from your home aquarium.
It has been noted by several respected authors in the aquarium trade that Clibanarius tricolor also eats cyano bacteria aka red slime algae aka blue green algae. Julian Sprung in his book Algae: A Problem Solver Guide notes that Blue Leg Hermit Crabs are very useful for the elimination of cyano bacteria.
Blue Leg Hermits are interesting to watch as they scavenge the tank for food, algae and more. They will often fight for food as well as new homes (in the form of available shells). Providing extra shells for your hermits is always advised.