I've used one similar to that. The differences are that I didn't use an airstone, and I placed a sponge inside the jar. The sponge will cause the air to flow through much more moisture helping to saturate it. Even still, it worked ok, but not great.

You mentioned that you're using a glass tank. Have you covered the screen top? There's a "sticky" in the husbandry forum entitled "Glass tank setup". You might take a look at that. Covering the top will help keep the humidity up. Jen uses foil and duct tape to close off the top. I use saran wrap.

Hope this helps.
Steve