How long have you had it? It's a different one to the other post? Leathers can take some time to acclimate to new tanks. I have a few and some regularly shed (all close over, no polyps and slime come out) every couple of weeks, others don't do this so often. If you've just put it in the tank it may not like the placement - move it higher perhaps (mine like a bit o flow) but it will take a couple of days to see whether they like it, because they don't like being touched so it can be a slow process finding its happy place.