elaborate:
I settled on the red legs based on info I read on the Garf site (my problem was green hair algae-they have different suggestions for different problems):
http://www.garf.org/greenalgae.html
They said: "This small crab is the best algae eating hermit crab we have tested. Clibanarius digueti feeds on algae that grows on the rocky substrate and mangrove roots. " and that's pretty much what I was looking for so I settled on these and they worked well.
So often you buy stuff, drop it in and it does absolutely NOTHING. I was thrilled when these went to work right away. That's all. They are probably the least pretty of all the hermits (the legs aren't all that red) but they do the job I bought them for.
I don't count my snails. I am guessing they would eat snails and sorry if this sounds cold but -meh- stuff happens...