I personally have 2 large leathers in my 125 reef....they do tend to shed about once a month, and at the same time for that matter. Its a normal natural thing, they're removing growth that might be attaching to its skin, as for why they might not be opening?...to much light (to close to mh's) maybe to much direct water flow....all are things that could be a variable in your tank....and sometimes when they get burned...there skin will look kinda dry....thats when you need to cut the light for a few days
keep up the good work guys i love all the pix!
~Chris