Sorry to hear about him! The white spots are quite possibly "ich" - the common disease that is found on fish that is brought about by (usually) high stress levels. You may want to think about a few things such as tank size, fellow inhabitants, and decor.
What size tank do you have? A good rule of thumb would be 1" of fish per gallon of water. That may be hindered by an overbearing amount of live rock and/or decorations in the tank however. How much room is there for your Grouper to swim? Panther groupers can get quite large; and therefore, need a good deal of room to swim around in.
If you don't have corals and sensitive inverts (corals, anemones, etc.) which I'm guessing you don't with a grouper, you could try treating him with copper based medications for "Ich".
The rockfall event may have had something to do with the sickness of your Panther Grouper; however unless it was a massive injury, the chances are slim that it caused the illness. It could be simply coincidence or other factors.
Let me know how he's doing in a few days or after you use medications.
~ Clifton | 
:mad: 
