I've had a tank become overrun with hair algae to the point that I gave up and tore down the tank. Once it gets a foothold on your rocks, it can quickly overgrow your corals and coraline algae, smothering everything in its path. My current outbreak has only grown on the LS and has not grown longer than a few millimeters in length. I stopped the growth, but it will tank awhile before my tankmates can erraticate it. Having visible hair algae in my tank is a scary thing for me, I've seen what it can do and I have a lot to loose if it gets outta hand. There are plenty of macroalgaes to give your tank that natural look and I currently have 3 types.