centimeter clear bug

[Viv]

Can't take a pic, its too small-appears to have legs, clear, about 1cm long that tapers toward the end. Runs along rock, up and down corals, doesn't seem to be harming anything. Its fast, and if I weren't starring at coral polyps I never would have known it was there. Any idea of what it could be? Good or bad? What to do about it? I've had pods on the glass-white. It doesn't look like them, if you could imagine it looks like a microscopic clear crayfish.

[VWD]

Just some other type of pod, I have some that come out and haul A** when I feed the fish, Thay are on the hunt for food also. Then the fish go and eat them. if they can catch them.