obviously, imo, the best way to rid of hair algae is to cut off it's fuel. either overfeeding, underskimming, dirty filters, phosphates from source water, or excess nutrients from some supplements can all be causes. one or more than one. i'd say look at what you are doing with your tank, and see if there's a possible cause from your own actions. this would be the best way imo, to eliminate the source of the fuel for the algae...imo.
also, blue legged hermits will eat the hair algae once it gets long. snails will only help keep it down once it's gone. i've had good luck with the blue legs and snail tandem, and you don't really need a whole lot of them. just a few small ones, and give them time. cutting your lighting can help, but ultimately you need to find the source the algae is feeding off of and cut it out from there. once you get it to stop growing, the blue legs will clean it up nicely. jmo, hth, good luck..=)
hey steamboat, i don't think scarlet crabs or emeralds are really known to eat hair algae. i have blue legged and red legged scarlet reef crabs, and have had an emerald, and the blue legged are the only ones i saw that actually ate hair algae, be it green or red. i had removed all of the crabs out of my 20g, because they were crawling on my corals, but hair algae broke out on a rock i got with shrooms on it, and i put a couple small blue legs in there and within a week, the rock was totally cleaned off =) now my snails tend to keep everything in check pretty good. i do try to feed as little as possible, and don't really add a whole lot of supplements either. also, i got tons of lighting that stays on for 14 hours a day. hth.