Apollo, my male White's Tree Frog, seems to have taken to rubbing his nose on the glass!

He's got a brown square between his little nostrils and I remember that my female arrived with a skinned nose when I first got her. I never put anything on her nose and it seemed to clear up in a week or so after she got settled in. His spot is much larger and I was wondering what (if anything) I can put on the spot on his nose? Should I even put anything on it?

I recently bought a fogger and have been running it twice a day (once in the morning and once at night) for about 30 minutes to keep the humidity up. I have a towel over half of the screen to keep the heat in as well. Currently, the temperature is 71.4 degrees Fahrenheit at the halfway point of the tank with the humidity running at 74% in a 24"x18"x24"Exo-Terra tank. Unfortunately, there is no background on the outside of the tank as I am in the process of working on a 29G vertical conversion.

Could not having a barrier there be what's causing him to do this?