Baby Red Eard slider????

I have this 2 inch Red ear slider turtle that has been basking for like 4 days straight and is completly dry. He only comes for ater when feeding time.He got bit by my other 3 red eard sliders who have killed a Re eard slider,Alligator snapping turtle,Midland painted, and a diamond back terrapin. They all ganged up on him and now he has missing cace scales. I think hes trying to recover but im not sure And i took him to the vet but he said he was to young to put shot in him to get better. I keep him in a 10 gallon tank for now until he grows a little bit to be with the other red eard sliders. Does anyone know why hes doing this? Thanks