So I've been battling an outbreak of what I think is green hair algae. I've tried many different things to try and combat it, but nothing outside of just manually pulling out clumps of it has worked. It does grow very fast, to the point I'm pulling out close to a handful weekly. I've worked with my local LFS with several recommendations. This is a 90g with a 29g refugium underneath. Light is 2x250w Metal Halides and 4xT5 Actinics. These run about 10-12 hours a day. I have a tang and a foxface, neither of them will touch it. I've tried 3 different sea hares, one of which seemed to nibble at it a little, but didn't really touch it either. I've tested nitrates, phosphates, nitrites, etc. and all come out as zero. I know that doesn't necessarily mean they aren't there and could just be getting consumed by the algae. I have put a bag of phos-guard in the sump about 2 weeks ago, also didn't seem to make a difference. This is a tank that I set up about 4 months ago, but moved everything (live rock, most of the water, corals, fish, etc. from a 40g that had been established for over 2 years.