I just bought a nice piece of live rock with a lot of zoos, various bryozoans and macroalgae on it. There are a lot of "buds", but only a small number of the zoos are open. The ones that are open are very healthy and fully open. Can anyone tell me why most of them would be closed? Is it possible that they are too small to be open? Also, I had a hitchiker on the rock. A snail that resembles a freshwater Ramshorn snail. It is black, has a spiral shell with a diameter of about an inch. Does anyone have any idea of what it is? It's hiding, so I can't provide a picture at the moment.