good day everyone. i have 5 motoro pups which measure about 4 to 5 inches disc diameter in a 100 gallon tank which later on will be moved to my pond. parameters are ammo - 0 , nitrite - 0 , ph - 7.4 steady no swings , nitrate - 10 ppm. these guys are fed 2 times a day with deboned chopped fish fillets. this morning i gave them their regular meal and then i went out to take care of some stuff. when i came back home tonight with lights off. i noticed that 2 or 3 of them were lifting their discs near their tail. i read somewhere that discs should almost always be flat on the tanks surface. here is an attached photo. any help/opinion on what this could be or if it is normal or not, would be greatly appreciated. thanks much