The mythrax can help with hair algae but it's more known for aiding with valonia. Believe it or not, hermits are best for hair algae. Primarily lefthanded and scarlets (yellow eye stalks). Urchins can also help but should be added with caution as most do not discriminate what they eat and few are safe for reefs.
, these are only going to cure the symptoms, not the cause. PO4
is what will fuel these types of algaes. Whether it be from the water source, foods or lack of export; you need to deal with that if you want to be rid of it permanently.