Indeed the best idea vamp! I had this ray in a 50g aswell till yesterday. I have a 3x50 rack, and it was in the bottom tank. I just hate the bottom tank in rack, have to lay on the floor to enjoy the fish.
When my two hystrix pups were born last fall, I moved them to their own tank. Get ready for this....... A standard 15 gal tank with a hob filter The tank had been running for about a year as a grow out tank for some eartheaters. The water, substrate, and filter material for the 15 gal all came from the main stingray tank. A few weeks before the pups were born, I used water from the ray tank to do water changes on the 15 gal tank. Keep in mind the pups were about 3.5" when born. I kept the pups in this tank for a few months.
I wouldn't use this small tank for pups of larger species though.