Have you ever researched high magnesium levels as a solution to hair algae? Check this out:
http://www.reefcentral.com/forums/sh...lgae+magnesium
Aside from that, all we have are some basic details from you about your tank. If you're not into trying the Magnesium idea, then take the time to write down all your daily maintenance, weekly maintenance, monthly maintenance...everything you do to your tank and how often. Include amounts like size of waterchanges, amount of food, dosing of any additives, etc. Also include brand names, and product names. List all specs - all testing from the last 6 months; ph, amonnia, nitrite, nitrate, phosphate. Also salinity, temperature, lighting hours, hardware, bulb brands, last time bulbs changed, etc. Don't leave anything out.