controlling hair algae depends on how old you tank is, if it is between 0-3 months i would say do not worry. but if older than you may have some problems.
1. circulation play a huge part you dont want trapped detritus
2.temperature shoul be kept constant and 25 celcius
3.old bulbs play a part
4.lack of competition, tanks with large amount of photosynthetic organisms (coral) make it harder for algae to grow (competition for nutrients). A tank with lots of LR and few corals is harder to maintain than a tank with the same amount of LR and lots of corals.
5.If you have nutrient problems you can try algae filtration (refugium), mangroves are also effective.
6.soft coral farming, some corals eg xenia have the same speed of growth as caulerpa and can be harvested removing nitrate, phosphate etc.
7. blasting the rockwork with a powerhead is useful as it sends detritus into the water collumn where it is possible for the skimmer to remove it.
8. water changes will lower nutrients that are harvested by the algae
9.animal control: copepods, amphipods, urchins, snails, fish, crabs, sea slugs, starfish can be used to control the algae
10.filtration: purification of top up water (RO/DI), activated carbon removes dissolved organic compounds from the water, dosing kalkwasser (calcium hydroxide) elevates Ph and precipitates phosphate, skimming removes organic compounds, uv sterilizer affect floating spores and filaments that pass through it reducing reproduction.