Not sure lol when I first noticed it was starting to split it was already like that, it was pretty neat!! Happens pretty quick, a couple hours or so.... I read up on nems slipitting right after, they say its hard to determine whether its splitting due to stress or because the tank conditions are ideal for it to reproduce. I swapped out a couple bulbs about a month ago, and the nem moved around 3 weeks after. Had been parked on that rock for over year until recently, doesn't seem to be dying, just moving around a lot so guess ideal conditions maybe..