What kind of substrate do you have in your tank? If the gravel or sand is course it will make microscopic cuts on there underside often not noticable. Then bactiria which is in all tanks has an oportunity to feed. This is probably why your ray will not sit on the bottom. As far as not eating all of my rays like to dig in the substrate to find food. If this hurts your ray might not like to dig and therefore not eat. I keep my retics with Discus. The discus seem to eat all of the food before it hits the bottom. I devised a tool that not only lets me feed each ray its own diet but also works to inject food into the substrate. get a large seringe and a long hard plastic tube small enough to fit snug on the seringe. Then heet the tube about 2 inches from the end and bend it about 45 degrees to be able to put under the ray. After a few feedings they will associate the tube with food and will eat whatever you put in it. Good luck but I would look at your gravel or sand before purchasing an expencive ray.