[reefgeezer]

Sometimes a particular coral just doesn't do well in a system. I wouldn't continue to make changes trying to get it to respond. You may end up harming everything else. Trade it for something that will do better in your system.

I have a tank that won't grow Zoas or Mushrooms for crap but Leathers do well in certain places. Smooth skin SPS corals just fade away but others SPS corals do great.

If you still want to try something, you might reduce your water changes and stop the GAC to see if maybe a little extra dissolved organic material might help.