I've had much much worse GHA than this and not had a single SPS coral perish.
So I disagree with the statement that algae will cause sps death within a two week time period, at the levels it is in this tank. GHA pretty much has to be touching the coral and growing over it to cause death in my experience. Otherwise we wouldn't have huge refugiums and algae scrubbers setup for nutrient removal. When you do go to remove the hair algae keep the lights the same, and use a tooth brush and filter socks, or do it in bucket of water change water. Leaving the lights on and manually removing speeds up the process of the algae depleting the nutrients it's feeding on IMO, your going to be scrubbing regardless, might as well scrub fewer times and remove larger quantities of algae.
I've had much much worse GHA than this and not had a single SPS coral perish.What you can run into is the GHA out competing the SPS for nutrients when you reduce feeding, which in turn causes the coral starve to death.
This is not to say that GHA can't create chemical warfare, I;m not knocking the idea of it at all, just dont think thats what this one is given my experience.
Here are my questions:
1. Are you running ATO?
(sps HATE salinity swings)
2. What is the Tanks Temp and have you checked for swings during the day with your ATI on?
(My 200 Gallon swings 1 degree with less watts per gallon than yours, anything more than 2 degrees is no good especially if the corals aren't used to it)
3. Are you losing these corals following water changes?
(If your using Red Sea Coral Pro the alkalinity spike from adding 12 DKH water to 8.2 DKH water could be causing the issue)
4. Have you left the system for extended periods of time without any sps to rule out bacterial infections, or pests?
I agree, i don't think the GHA is the direct culprit, but it's a tell tale sign that something isn't quite right. To what extent that's playing into the SPS die off, i haven't a clue, but I would definitely resolve it at the root cause so at the very least you can clean up the system and remove it from the potentials as to why the SPS aren't making it.