I've kept the red form of Diodogorgia. (BTW I think I'm the one who suggested rubbing the algae off.) Their polyps were closed at least as often as they were open. When they did open, a few polyps would open first. Then, usually the rest would open too, but sometimes not and then they would just close up again. It didn't seem to me like they opened in response to food in the water, but rather that they just opened at random times. But maybe I wasn't paying close enough attention. There are some threads from this board about how to take care of them. Delbeek & Sprung Volume Two has lots of information about them too. I have a Caribbean tank and would love to have gorgonians again, but I found the non-photosynthetic ones difficult to keep. Sea Critters sells aqua-cultured gorgonians which they call "Eco Gorgs," including a number of photosynthetic species from the Caribbean. I have heard only good things about them so far, but I haven't ordered any yet.