pristine stable water conditions and the proper lighting, and light (small) twice a week feedings, brine size, healthy nems never need fed, give it all the above and it should produce more zooanthellae which is the color in a nem. The brighter and deeper red it is, the healthier it is. What is your lighting and tank information. They produce their zooanthellae from feeding off your light spectrum, thats why lighting is so critical to their survival.