I think he explained the problems with using too much GFO pretty well in his 7 points. Most of it is related to stress on corals of a sudden drop in phosphates, organics, and trace metals, etc. It sounded like at least some corals even need a bit of phosphates (at very low sea water levels). I run a reactor but only add the recommended amount to avoid problems. Since the amount recommended is less than what's recommended to run the reactor properly I add carbon too (per the reactor instructions). Since I already fight low pH, GFO can also drop pH, and I don't need that.