If you water quality is truely good then it may be something else. Does your clownfish suck on the tenticles of your anemone? I have read somewhere that certain clownfish don't host in specific anemones in the wild but will host in captivity (just can't get enough). Because they are not naturally paired, the clownfish will suck the micus of the tenticales to create a resistance to the sting of the anemone. My clownfish do this and it causes the anemone's tenticales to become disfigured but cause no visable damage to the invert. Hope this helps!