Happened to my pup when he was new to the tank. Kept lifting the front of his disc up and i was kinda worried. Went to research a little to be safe and found a thread that this guy had saying that his ray started doing that when he accidentally dropped something in front of his tank which spooked his ray, making it burst all over the tank and then the disc lifting started. So i guess that happens when the ray is stressed and my probably had that cos he was new to the tank and stressed. My ray is perfectly fine now and isnt lifting the front of his disc like that anymore. Hope this helps!