Green Hair Algae

[Matt]

We're battling a rather unnerving outbreak of GHA. So far, we've taken some steps as recommended by others on this board and elsewhere.

1) Skim wet; done. We're taking about a cup of green water out of the skimmer daily.
2) Reduce feeding; done. I'm actually worried for the fishies, but they are coping so far.
3) Test water; done. All parameters we can test for are nominal. Mg is a little low-normal, but everything else is OK.
4) Raise PH; done. We brought PH and Alk up to high-normal.
5) Manual cleanup; ongoing with weekly water changes (I might start another thread about that adventure). Huge amounts of GHA are manually removed every week. Daunting.
6) Compete; We bought some Chaeto, set up a 27W 6500PC bulb over the sump (27/7), and are growing that out. It has more than doubled in size, but the GHA doesn't seem to notice. We now have GHA in the sump too.
7) Reduce light; done. Shortened MH time to 6 hours daily.

This stuff is extremely aggressive, and is choking out some corals. Does anyone have any other tips? I've read that complete darkness is one option, but won't that also kill or heavily stress the corals?

Tips, suggestions, expert advice - all welcome.

Matt