Rays are a nice addition to go with the aro, but again with both your going to want to do a major up grade from 75 gallons. Rays need a much wider tank. if your going to go with a motoro ray, which I believe to be one of the smallest fw rays, its going to have to have to be atleast 30" wide and with the aro your going to have to be 6' long. And rays need crystal clear water paramiters. Rays are not big on big water condition shifts so just have to becareful of that. Personally I think rays should be bigger then they are in this hobby just know what your getting into before you get one!