Poorly grey tree frog

[elly]

Those are all good guesses. Sadly I can't diagnose for you, but if soil from the outside was put in it might be nematodes. If he seems to have patchy skin, or incomplete shedding it might be chytrid or some similar fungal disease.
I'll be honest that it doesn't sound good. If there is a vet that would be willing to see a frog in your area, that would be the best option. Or you could look into anti-fungal treatments. However, those are likely to cause the frog some stress and if the frog isn't suffering from a fungal infection, would do more harm than good.