I keep Rays with Koi with no problem, just be careful on how you handle them, and make sure that none of your fish will be aggressive twards the Ray, It could be the fish's last mistake
I was thinking along the line something like discus, rose line sharks, ghost knife, and maybe some sort of sailfin molly so when they breed everyone gets a treat. Another question i've had is can you have live plants with rays? I've that eat them to the root ,but i just wanted to know if anyones had luck with live plants and rays?