I have been keeping rays for a few years. The blue spot rays (Taeniura lymma) are difficult to feed and usually die because they refuse food. Every once in a while you hear a success story, but your chances of getting one that eats with gusto is not that great.
However, there is another type of blue spot ray Dasyatis kuhlli that is "slightly" better but still very difficult, especially if you are not used to handling rays and the kuhlii needs a lot of space. A California round ray is a lot easier to keep than either of the blue spot rays that I mentioned.
Tank Size - Your tank would be ok for about 6 months with a baby California ray but after that you will need more room. They do not require massive size tanks but they do like to move around and will use every available inch of the tank. You current tank is way too small for the kuhlii for sure but the 48 x48 should work.
Rays are also very messy. They eat a lot, need to be fed daily and require a big skimmer and a good amount of water to control ammonia. For example, my adult California ray eats about 3 large table shrimp a day or sometimes 5 to 6 silversides etc., depends on what I am feeding. My kuhlli is a very picky eater. It only eats PE Mysis and lots of it. The problem is that a large amount of PE mysis can easily pollute a tank.
When I first started keeping rays, I could not control my nitrates, etc. I was doing large water changes weekly. I tried 3 different skimmers and finally settled on a Bubble King.
I am not trying to discourage you from keeping rays. They are a lot of fun! Just giving you the heads-up. I had to learn the hard way.
