Ok, I ask because lots of carbon seems to help pinched mantle, and GFO seems to be a trigger sometimes. Looks like you are doing ok in that area though. Time for a dip! Pinched mantle is a pretty serious disease...best to catch it early!
What lights are you using? How long has the tank been running? What are your parameters? Cal, alk, mg, temp, ph, salinity, nitrate, phosphate? Any ammonia present?
Be sure to match pH with a digital meter, match temperature as well. Use dechlorinated tap or RO water...preferably the latter. I would advise 20 minute dip, but here is a link that suggests a 30 minute dip:
http://reefkeeping.com/issues/2006-09/jf/index.php