ostrow & others, hang in there!
I followed this thread a few years back. I might have posted once or twice to it when I tried algaefix for my GHA problem. It didn't help. It made the things worse. Lost my chaeto & rendered my refugium useless, while the GHA just kept growing.
I battled GHA for over 2 years. I bleached a new set of rocks, cured them, swapped most of the old ones out. I kept pulling GHA out. Tried different algae eater fish, inverts, even sea hares. For a while tried GFO, but it was too much mess and maintenance for me. My phosphates test kit always showed very low levels, nitrates were 0 as well. I guess the GHA was consuming them fast enough.
Well, today, my tank is algae free. What seens to have worked for me in the end, was to let the tank run out of nutrients:
- I kept running the skimmer aggressively
- I used only bio-pellets and not GFO since the bio-pellets were low maintenance and fit my busy schedule.
- I re-populated my refugium with some chaeto & a couple of mangroves. In time the GHA started mixing in between them, I did regular trimmings, but I let the GHA live there.
- I used a normal/minimal CUC, maybe 20-30 hermits and around 10 snails (most throcus, my favorites). My tank is 125G.
- I reduced the number of fish, gave away my medium to large tangs, my foxface, I kept only 3 fish that kids got attached to, and a few smaller ones, about 6-8 in total. I fed them once a day a small amount they could finish in 10-20 seconds.
- I kept pulling GHA out of the rocks, used a toothbrush to clean the rocks, threw out some compromised rocks & even some birdsnests that got covered all up in algae.
- I let the tank settled for over 1 year, no new fish, no new corals, no changes other that some minor landscaping from time to time, pulling out GHA and doing water changes when time permitted. When doing water changes, I used a small powerhead to blow the dust and dirt from between the rocks and hidden places. I made sure to use only good RO water, I used the same salt (Reef Crystals), really trying not to change anything in the tank's parameters.
One day, I suddenly noticed that the GHA doesn't grow anymore on rocks that used to be almost fully covered. And from there it was easy

. It kept regressing until one day I could not find any in my DT. I still have some mixed with the chaeto and the mangrove roots in my fuge, but even there it seems to be slowly regressing.
This is my tank today, fish and corals are happy, while the algae is gone.
https://www.youtube.com/watch?v=lrFa0BKqg24
So there is hope. I was in the same place, almost ready to throw the towel in. Things will get better, just takes a lot of patience & stability. See what works for you and stick with it.