its a frag but it was healthy when i got it for a couple of weeks. lately i dont see any of its polyps out now. it still remains its purplish color so it didnt bleach yet. im just mainly concerned about the polyps not opening. could it be RTN or STN that i've been reading about? what is STN or RTN even? is there anyway i can cure my birdsnest? its my favorite coral in my tank... =[