They tend to close up and look sickly when they are expelling waste (pooping) as well as when the lights go off. If it is new, try not to move it too much. For the first week, they are very stressed out and very unhappy. If they don't like where they are, they will find a place. If you notice it moving around a lot, then it means there is something wrong with either the water quality, or the lighting, and that is when you want to take action. Otherwise, feed it regularly, and let it do it's thang! ;-)