Cali rays should be in a very fine sand bottom, with very low temps( in comparison to an sps tank) wth ALOT of open swimming room. I think you have an AMAZING SPS tank and for you to have kept both, one of them wasnt going to do well( either the sps or the ray) for alot of various reasons( temps, sand, flow, swimming room) but i do commend you for tryign and especially for bieng honest with everyone so that more people dont try this combo unless they have all all the correct params for the ray. Rays are messy and crazy swimmers if i had your tank iw ouldnt even want to risk the chance since it is such an awesome tank.
Loosing any animal sucks and im sorry to hear about that but the bright side is your tank is very nice!!