I am kind of having/had a similar problem.
I had all my rock and corals get covered with a thick matt of hair algae, it was about an inch long. It looked just like a field of wheat before it turns amber, billowing in the breeze, grew right up each colony of sps and killed every one. I even had two fish that gorged on the stuff, but they could not keep up. We actually took the display tank down it was so bad and kept the sump tanks running in the basement fish room while we decided what to do, get out of the hobby or persevere. I know it is really tough Rob! I am sure it is even worse when you don't have the option of shoving everything out of sight like I did.
Anyway, I did major changes, removed all the dirty sand, did a massive massive refugium upgrade, cut back feedings, went from MH to PC (there were other reasons behind that move too) added snails, added a DI cartridge to my Ro system. I even added an extra hang on skimmer I had laying around for extra measure!!!
The crazy hair algae is gone, I still get fuzzy algae in the places my tang cannot get to and in my fuge, but what concerns me is I am seeing a ton of detritus all over my rock. I was not able to see any of this when everthing was covered with the thick hair algae, but when I think back, every time I pulled out clumps of HA, it had what seemed like soil built up underneath. I truly feel that this dirt coming out of the rock was a significant contribution to our algae problem, and that the big changes we have made have helped, but if we stopped for a minute with the extra skimming, waterchanges, and heavy macro growth, then the HA would be back in a heartbeat.
The detritus piles up underneath the rock, and I have been stymied about where it all is coming from, one day after blasting to rock with a powerhead, it's all dirty again. I hardly feed, and when I do I am target feeding the anemone, every else gets scraps or a little macro algae. We also always suck out detritus every time we do a water change (which is often) but still, there is junk all over the rock.
Some of my rock is 7 years old, the youngest rock is almost three, and I am now thinking I may have "clogged up" filthy rock that needs to be "cooked", I plan on reading up on that more and trying it with a few pieces to see how it goes.
Anyway, I don't want to sideline your thread, but I thought something from my experience would be helpful.
I wish I had pictures of the algae, it was truly rediculous. I totally understand your frustration.
). Generally you're dealing with much less light intensity. Light + nutrients = algae, so the more light you have, the lower you need to keep nutrients in order to avoid problems IME.
