I see coralline algae on the left; hair algae top and center; a snail on the right. I'm guessing you mean the hair algae. It's a product of excessive light and/or excessive nutrients in the water. Consider reducing your lighting schedule, reducing feeding, switching (if you don't use it already) to RO/DI water. Also consider growing macroalgae such as chaetomorpha in a sump or refugium, and possibly adding some kind of clam. Either of these will remove nutrients from the water. And, of course, increase the frequency of your water changes to export excess nutrients.