Stingrays need a LOT of room. There is a fish store on the north side of columbus that has them in a 400 gal
floor tank. One thing that I noticed while watching them is that they don't really swim around; they stay on the 'ground'.
A 75 gal
tank only gives them 6 square feet to move around in. When those rays hit the 12 inch mark, they will be really crowded.
I once thought about doing a ray tank but realized that I wouldn't be able to unless I built a custom tank with a large width and depth (front to back) to accomodate them...