I just recently bought a Motoro stingray that is about 5-6" and i have notice today after a water change that he has the triangle thing on the tail where it meets the base. His forehead is also hollow. He isnt really swimming around much or eating much either. Maybe a little piece of bloodworm but not a lot. Does this mean that its too late? Or is the ray just really stressed right now? My ammonia and nitrite is at 0 and ph level is at 6.5