I had 2 Motoro's that use to do that. I would do my normal water change and they would jump up above the water that came out of the spray bar and turn it's disk like that and just float. When I first saw it I was like WTF?!?!? is happening? So, I touched it and moved it around the tank and it didn't even try to sting me or anything. I thought that they were just playing in the water current that came from the spray bar, but that wasn't it. About a month later I found 1 of them dead in the corner with curl and the next day the other 1 died with curl. They were both fine and eating well. I tested the water and I found out that I had a huge ammonia spike! Oh, and they were the only ones in the tank, and I never gave them live food.
I'm sorry to say that if you don't watch that Ammonia, you will have a dead ray within a month.
GL and keep us updated!