Okay, I've heard all the same replies (fixes, tips, etc.) that you have received from everyone. I also have a 46 gal. tank added a refuguim and started to do alot of water changes, etc. Problem was not going away and I was getting very flustered by the whole thing. I was even ready to shut down the whole tank. But I got a sea hare (they are ugly and look like tards), but man did it work. Hair algae and seaweed are the only things they eat, so once the hair algae is gone, you need to get dried seaweed and put it in the tank every now and then. These things have huge appetites and I can't believe how fast one went thru all the hair algae in my tank. The only thing you have to be careful of is to cover all suction devices (skimmers, pumps, etc) with sponge like material (cause it will get sucked up in the intakes). I went to my local fish store and brought a large pack of a square filter type sponge, cut an x in the little pieces I cut off to cover the intakes and all was fine. Some people will tell you that the sea hare will ink your tank. I have not had that happen even when my first one got sucked into the skimmer pump. They are pretty cheap to get, I think Pets Plus around here sells em for $19.99.
Good luck.
Cindy