Quote Originally Posted by Sanguine View Post
That's precisely the problem, its knocking itself against the inner surface of the tank! And it's not just one specific area either.
Hmm, its about 5cm in length. Also, is the reddish colour abnormal?
Your frog is way to big for that tank. You might want to give Frog Forum - White's Tree Frog Care - Litoria caerulea a read. It recommends an ~80L tank for an adult (the more the merrier though). Your tank is about 9L and your frog isn't far off from a full sized male.

The reddish colour could just be caused from it climbing on the glass all the time. Is it still red after it's been resting for awhile? Was it this red when you first got it? Hopefully someone more experienced with frog diseases will comment.