they are not hard to keep at all. Just adhere to good fishkeeping contact such as great water quality and a healthy diet of ghost shrimp(for young ones) and feeder goldfish, shrimp, worms and such food for adults. and u got yourself a nice fish.
you can go two ways i have seen with these rays. 1-is a bare bottom tank, this requires a bit more water changes as the debris on the tank bottom is more visible or 2- put a thin layer of subrate, not too course for small specimens with lots of free swimming space along the tank floor as this is their zone and they stick there unless they wonder up on the side panels of the tank.
Tank mates-preferable non but if you do choose non boisterous fish that stay in the upper levels of the tank and dont bother the rays. small fish that can fit into their mouths are a NO.
its great watching how gracefully they hover along the bottom of the tank.