Leather corals go through a stage periodically, which may be more numerous or less depending on a number of variables. This stage known as molting or sloughing is similar to that that snakes go through in shedding their skin as they grow.
Leathers will form a mucus coat on their oral disc as a way of removing detritus, parasites, algae, sediment and possibly as a way of growing.
I don't know if this is actually what is happening with your leather or not, without seeing pictures.
Leathers can develop various diseases not limited to white and brown band disease and tissue necrosis! Hopefully you don't have that going on... _________ 125gal.w/Mag9.5 return(dual megaflow)>Mag7 pump Aqua Cev180skimmer.Wave2k Hamilton Reefstar(2)250watthqi(mh)pend.a Yellow, Naso Tang Red Lip Blenny Percula Clown Demoiselles Niger Trigger F. Wrasses Ceriantharia Orn.Shrimp and Stars Hermits Queen Conch asst. snails> Stars Zoos shrooms Montipora Brains Gorgonians Favia Turbinaria(large+small polyp) Acropora Xenia Tridacna (CroceaMaximaSquamosa) Leathers <35+75gal.reef tank as well> 
"IF THE PHONE DOESN'T RING...IT'S ME"  jb  |