Sea Hares do indeed eat hair algae,but will starve to death after it is all eaten.If you have 2,it won't take long.Start looking now for someone who has an algae problem so you can pass them on to a food source when your tank is cleaned out of algae.We had one and it cleaned out the hair algae out of our 125 reef in less than a month,then disappeared(died)a short time later.We tried feeding it sheet algae like our Tangs eat,he ate it,but I guess that wasn't enough.Good luck.