I dont agree to first part. But its your experience and opinion and I respect that
second part. the articles above show what happens to TOCs when GAC is ran part time. I think SPS like stability than changes in TOC ...
but let me ask u. why run GAC once in a while anyways ? to help with yellowing and removal of toxins right ? what if you used the 1/3 of the amount instead and left it in for a month ? GAC has a saturation point
about loosing color, i have touched on that above as well, some are acid washed and alot more potent. so ... check boomers posts with this regards. I run REALLY low nutrients ... if I use ROX carbon, my corals will become WHITE within hours. some may even die. but I use less potent stuff at half dosage with no Issues. it actually improves the colors and PE. I use seachem matrix currently.