Hello and welcome to Fishlore
I moved your thread to a more appropriate forum where it should get more attention.
How long has your RT had this hole in the tail? Did it start small? Was it discolored at anytime first.. or did you just notice it one day.
If it is newly discovered, its possible that he injured it on something in the tank or was bitten. If it started out small or discolored it could be another problem such as a disease of some type.
Do you have any photos of it? And can you let us know what else you have in the tank with him?
A lot of questions but the answers may be able to help others help you determine what may have happened to your RT.
