Have you tried the crumbled up newspaper trick?

You could aslo set up a smaller tub and switch him over to it, sometimes the change in scenery sparks something in them. If you prefer the glass tank, when you have him eating again you could switch him back and try your luck with it.

And then there is just the fact that sometimes they just don't eat. I would watch his weight and make sure he is still urinating and at least maintaining his muscle tone.