Green hair algae problem

okay guys,so, my 15 gallon is having some serious hair algae problems! i just cant keep up with picking it off the rocks anymore :cry: i am using RO/DI water only, do a 25-30% water change once a week and the tank is out of the way of any direct sunlight i havent yet used any phosban or other phosphate removers but think im going to have to resort to it,anyways i would still like to get to the root of my problem so was wondering if anyone here has any ideas what it could be.
thanks for any advice. :D