Who has hair algae? The best way to eradicate hair algae is to figure out it's cause, and change whatever it is you are or are'nt doing that is causing it.
Reasons for hair algae are too much nutrients..so: overfeeding, overstocking, inadequate or wrong type of clean up crew, poor flow, detritus build up on rocks, inadequate protein skimmer..or in the case of a nano...not doing weekly water changes, not using airated RO/DI water with 0 TDS, bulbs that need to be changed....
If this is a nano that has hair algae, there is no appropriate invert or fish that will eat it. I would suggest manual removal of as much as possible, and address any or several of the concerns I have listed. The use of a turkey baster {kept for this purpose} to blow off detritus & leftover food before water changes can help. It gets down in the cracks & crevices of the rock and fuels the algae growth.