IMO there are a lot more factors going into whether a tank is ok with GFO/GAC use or whether it will bleach corals. It may or it may not.
I started my tank running both and found all my SPS bleaching badly. I eventually took both GFO/GAC reactors offline and my SPS colors have returned and look better than ever.
A couple factors I have gleaned from various threads (do not confuse me with an expert!):
1. SPS consume phosphates and nitrates. If you have zero, your corals will not be happy. You need to maintain at least a low level of each for optimum color and coral health. What those levels need to be varies depending on who you talk to.
Personally I run Nitrates 2.5 - 5 ppm and Phosphates 0.00 - 0.02.
2. Lighting depends on your Alk & Nutrients, stronger lighting is needed for high Alk & high nutrients, lower lighting for low Alk and low nutrients.
Personally I run two Radion XR15w Pros at 100% intensity and Alk at 8 - 8.5.
3. Coral feeding is needed if your nutrients are too low.
Personally I feed Reef Chili, Reef Roids and AcroPower
4. GFO & GAC should generally only be used if your nutrients are high and need to be controlled, or if you're crazy anal and don't want any algae in your tank.
While mine are both currently shut down, I am glad I plumbed my reactors in case I need to run them in the future.
What I've found is that you need to find your balance. Run your lights as strong as you can without bleaching your corals. Monitor your Nitrates and Phosphates, and adjust Alk, Lighting, and Feeding accordingly. Too much nutrients you can increase Alk & lighting or reduce feeding or use GAC/GFO.
So many variables and things to balance and every tank is different. What works for your tank may not work for the next guy/gal and so on. But eventually you will find what works for your tank.
Feel free to agree or tell my I'm full of it! :spin2: