Which species of plate is it? Heliofungai or Fungai? Has it been damaged or stung by any nearby coral? Does this "brown stuff" appear to be algae or cyano, or does it seem like a discoloration on the coral?
When I bought an Orange Fungia sp. from the LFS, I noticed that one portion of the coral had been stung by a Euphyllia sp.
After I took it home, it had no polyp expansion for over a week and the skeleton was showing on one side of the coral. Algae started to develope on the dead area of the coral after a few days.
Here's the coral on 11/11/03:
http://reefcentral.com/forums/attach...postid=1980227
Here's the same coral 12/18/03:
Give it time and good water conditions and it should come back fine.
Graham