I think people tend to overuse both GFO and GAC.
For GFO I use about 1/8 cup per 100 gallons to start with. On my 180 gallon SPS I only used 1/4 changed out monthly. On this tank, when I was using it, I stated out with 1/4 cup and as time went on I ended up using just under 1/2 cup.
For carbon, regular carbon I used to use 1 cup per 100 gallons. Half that if I was using ROX carbon. I never had problems with those amounts. When people have problem using carbon, I don't think it is stripping too much nutrients from the water rather it is clearing up the water so more light gets in the tank and you end up with bleaching. I run ozone on my tanks for water clarity so the effect of carbon on water clarity is less than some others who do not run ozone.
Bleaching IME is from giving the coral too much light too quickly, basically not acclimating it to your lights. Browning is just to opposite, not enough light. When I am placing corals in the tank. I start it in the bottom and if it does not lighten in 48 hours move it to the middle and do the same thing. If your corals are at the top and they are still browning I would look to see if there is enough light, if so, something is out of sorts with the tank.
Bleaching and browning was my big problem for the last few months. Basically all I did was water changes and kept the tank as stable as possible. People forget that you can start a tank brand new and as long as you can keep the paramters stable you can get good coloration with SPS right off the bat, tons of people who upgrade their tanks do it all the time. So when things are not working start doing water changes.