A rule of thumb that I have always gone by to distinguish between photosynthetic gorgonians and NPS gorgs is the color of the polyps. If they have white polyps, like the popular orange and red gorgs, I avoid buying them, because they are NPS. Brown polyps are usually photosynthetic and easier gorgs to keep. Personally, I have not run into an instance that this hasn't proven to be true. Certainly could be exceptions to the rule.