From your pic its hard to tell whats up.....it doesn't look entirely healthy.....the stuff you describe may simply be its waste....mine releases a stringy looking substance now and then.........but I'd be concerned more about the overall welfare of your coral......it looks like its not fully inflating and may be receding................I'd be concerned if mine was showing as much skeleton as yours seems to.......try lower current location and maybe a spot with more direct light........do you feed yours directly...mine really does lots better after a meaty meal......hope this helps a little