About 10% weekly, I skimmer runs wet and about a gallon a day of saltwater gets replaced each day with 10 gallon change weekly.
Did you mean RO water? If you are replacing saltwater daily your Salinity may be off.
If salinity is not the issue I would start feeding the coral with Oyster Manifique or something similar before taking the Carbon and GFO off line. Im pretty confident if all else is in order you will see better PE.
How well does your cheato grow with nutrients being low from the GFO?
I only replace the gallon of saltwater my skimmer puts out, as I said it runs very wet. I do add RO daily and check my SG (1.025) daily.
My cheato doesn't grow very well, but it does.
I feed my tank, well. Put I don't have any nutrient problems with all the export systems in place. I only get a few small patches of algea on the rock from time to time.
Feed the coral and see what happens.
SPS not extending polyps can be pretty mysterious if there are no pests. I had this happen in my own system recently. My frag of palmers blue milli had polyp extension after the tank move, then about a month later it totally shut down, nothing for at least three weeks, not at night or during the day.
Not sure if it was related but the lack of PE coincided with turning gfo/carbon online and taking it offline, in addition to a massive increase in feeding (PE came back after feeding and discontinuation of the gfo/carbon).
For what it's worth I've been dosing oyster eggs or feeding a "cubes" worth of homemade food each night. usually one nice squirt of the oyster eggs, maybe 1 tsp??
Now that coral is looking like the rest of my acros and has excellent PE.