For hair algae, a 2 pronged approach has always proven the most successful for me. it takes usually 2 months but maybe longer if your rocks have lots of bound up po4, but afterward hair algae shouldn't be much of an issue. Let it grow (except where it would harm your coral, if you can, move it for this part so you can get rowdy with the rocks) until it is about 2 inches long. by the time it is that long and dense, the outermost part is starving the inner most part for light. working in patches, pull as much as you can from the rock, and where you have just pulled it, place a few snails, either astrea, trochus, or turbo (urchins sometimes work well here too) right on the freshly bare patch of rock. They will clean up everything you missed and in a few hours that spot will be cleaner than clean. if they do miss a spot, hit it with a toothbrush. when you damage the algae i don't know why, but in my experience they ALWAYS find it more palatable, to the extent that when you are doing touchups later on they will invariably seek out where ever you have just cleaned. Repeat this process a few times and within a few months, you will find that it just stops coming back. This has worked repeatedly for me when setting up new tanks with dead rock, or after introducing more new dead rock. Yes, the tank is pretty ugly for a while, but this WORKS. If you lean into the curve with hair algae it will grow hot and heavy and then be done, vs stringing it on for a year fighting patches here and there. Just make sure you aren't pouring gasoline on the fire with your feeding habits by overfeeding(but also don't starve your fish!).