I happened to be walking by the tank, and this guy just looked so happy, I thought I would share with all of you. If you don't have a duncan in your tank, you really should consider it. They are fun to watch, easy to keep, and every once in a while (like now) make me look like I know what I am doing!
It's an iPhone pic, so squint, and it looks less blurry...
I have a 3 polyp duncan frag from the Trop, that never opens anymore. I bought it about a month ago, it was open for the first week, and now nothing. It doesn't look like its in bad shape, it just won't open. I have mainly SPS, and all the frags are great. I also have a decent sized goni that is always open. I don't understand what is going on with the frag. All of my parameters are in line, and all the other coral is doing great.
Have you tried moving the duncan to a different spot in the tank? It may be getting too much light. This was the case for mine which stayed closed for days; after I moved it, it opened up overnight. It may also be contacting some coral around it that it does not like. One of mine was retracting because it was contacting some kenya tree. In my experience, duncans are really non-aggressive and need space from neighbors.