My lfs got a motoro in for $140 and it is fat and healthy but everything i get from there dies within a couple days(except my black piranha). I really want it but i don't want it to die.
Sounds like improper acclimation to me. One of my LFS keep their tanks picture perfect. Acidic water for fish that need it and basic water for fish that dont. They will tell their customers if say they buy an arrowana from their S. American tank with a Ph of 5.8 to drip their new fish for an hour or so if they are adding the fish to a tank with no special measures to keep the Ph that low. If not the shock will kill the fish in a day or two....not right away.
Ask them if the fish dies, can you bring a water sample in within 3 days to show that your is water is good for the ray and that they or the distributers are the problem. Your fish acclimation is far, far more extensive than mine and the rays i've introduced have been OK.
Just ask them because you never know. If you don't ask you don't get.