Definately try to find the root of the problem. Most likely, too many nutrients from uneaten food, clogged filter pads, recent livestock deaths, static sand, on and on. In my own algae battles, I've found a combination of treating the root cause AND having algae eating critters to be a good method for treating hair algae. The sea hare is a good choice, as long as you haven't also got dinos. Once the algae is gone, you'll need another home for it.
Urchins are also a good choice especially since they can remove the top layer of the rock and really eradicate the algae roots. Sometimes, if the algae is too long, the sea hare can't eat it. Doesn't seem to be a problem with an urchin. I personally prefer the short spine black urchin.