Hi Snowy falcon:
One trick I learned from reading Slack's books is that if you want a large ceph, you should not give as much light. Red cephs are more colourful but for some reason, they don't grow as big as the green cephs. So the trick is to get them green first and then give them as much light as possible.
Another thing to remember is that some cephs remain green no matter how much light you give them.