Another cool thing about them is that they "swicth off" the "Rummy Noses" if water quality declines. Or so I've heard. Kind of like a Canary in a coal mine.
Yeah, they are great. And I do definately see their red drop off when I do a water change; they are very sensitive druing water changes too and you should treat your water before you add it back into the tank to prevent any stress.