1. It looks like there are three in there, one hidden behind the cup?
2. A couple of my males have a slight pinkish tint to them, similar the one in the middle of the tank, almost like there was a pink convict in their bloodline at some point.
3. Another thought is do you leave that light on all the time? Mine are most active in lower light conditions, like now, just the light from my 60 and two monitors shining on them and they are moving sand like they are natural born construction workers...