Green hair likes phosphates, certain spectrums of light, proteins and seem to prefer areas of low flow (not always).
Measure your phosphates before introducing a phosphate magnet.
What does your skimmate look like...assuming you have a skimmer. (too many proteins in your water column)
What lighting do you use and is there any direct sunlight? (yellow light)
How long is your photo period? (reduction of photo period may be in order)
What do you feed? Flake food is usually high in phosphates (seaweed).
Pull off any hair that you can with your fingers trying not to let it float around in your tank.
Hope this helps.