Yes that is Hair Alge.
Emerald crabs are supposed to eat it. As well as several types of snails. Also some tangs will eat it. (usually bristle tooth, but i'm not sure)
what are your tank readings. Are you using RO/DI water.
The hair alge is indicitive of hight levels of nutrients in your water. I have found though i have no readings for Nitrate, Nitrite, and Amonia I still get hair alge because I use tap water. (phosphates) However, the level of hair algea I get in my tank is not to the level that it is a nusance.