...Are you sure it's not fungus? Because if it's white, somewhat short and fluffy (think cotton candy), then yeah, that's fungus. If that's not it, could you describe it a little more in detail please? And where is it growing?
Could be hair algae (the really fine one) OR some kind of fiber debris (the stuff that makes dust bunnies if you have a LOT of them). Do you have carpeting where your aquarium is at?