Id say that your best shot is an hystrix/wallacei. And to stay on top of your wcgame. Rays produce more waste then any other fish. If you can get your hands on a bigger tank then its better situation to get a ray or two.
Depends on the ray! I have a male hystrix/retic hybrid that is full grown at 5" diameter fully rolled, and a female same hystrix/retic that is full grown at about 8" in diameter. I have them in a 120 gallon tank at 48" x 24" and they will stay stay in that tank for life.