Are they housed separately? If not, they should be. I'm a firm believer in housing cresties singularly. It's easy to know how they are doing and monitor them. Also, a male and female will breed and complications can arise if either is not to appropriate weight, ei: female becoming egg bound, stress, injuries.
Also I really don't like that the red light is actually inside the tank. I fear if your crestie jumps onto it, it could burn them very badly. Perhaps this is the injury...?
If the tank does need additional heating to reach proper temps please provide it from the outside of the tank.