You should really do some research before you throw more money away..
You can't just take rays and throw them in with random fish, no matter how 'peaceful' you think they are when you are watching them. The atmosphere of the tank can completely change at night, once peaceful fish can become demonic in disposition(RTC). Cichlids and Stingrays should not be housed togethor, unless you know what youre doing. You should quit buying rays and sticking them in under-sized tanks, with in-appropriate tankmates..
These are hard animals to keep. They are not a gluttenous catfish, or a bullet-proof cichlid.
Perhaps instead of spending more money on killing Rays, you should put those funds towards finishing this 1300g DIY tank I keep 'hearing' about.. Then, after you've done some research and decided if rays are appropriate to go in the 1300g tank with the tankmates you have, (You do realize RTC get 6 feet in length and will eat anything?), try to purchase one that is large and well-acclimated for the abuse it might take while you 'learn your lessons'..
After you killed that Motoro, didn't I tell you "Tank First, Ray Last..".. but what do you do, go out and just buy another Ray without knowing anything about it, throw it in an undersized tank, and aggressive tankmates.. Then come say "Help, Help, Help, What do I do?".. When it's getting obvious you don't want to listen or do research, just wanting immediate satisfaction.
PLEASE, do some research and make educated purchases.