Here I come giving some counter advice, not against the indoor pond idea, but against keeping a ray there,
1. Freshwater rays are poisonous animals. I don't know how big is your room but I believe there is a great risk of someone coming barefooted and steeping into the pond. Even you, in the middle of the night walking half asleep going to the bathroom, could fall in there.
2. Normally, rays will do fine in a 2 feet deep aquarium, and probably this would be required in you pond too. I don't know if you are willin to biuld id so deep.
Just 2 concerns that come to my mind. The project is awesome, but a
venoumous animal is, IMHO, not the right choice to keep in the bedroom.
And also, rays look awesome when looked from the top.