Hmm, are you sure it is all wired up correctly, sounds like a floating pin (on a digital pin!?)
Try the code with a small piece of foil or something first to make sure it is working properly. I would not have thought that the tube would make much of a difference.
it's quite reliable with a small bit of foil. it works VERY well actually. i would have thought the same about the tube, i didn't expect it to be that much different at all. i'm sure its hooked up right. i'm using an alligator clip to attach to the tube. when i just clip it on foil (or read directly from the alligator clip itselft), it's fine. but the tube doesn't work at all. seems strange to me.