Diamond back terrapin needs help!

[Darklightning07]

Hello ! I recently got a diamond back terrapin and noticed some yellowish scar like on her back foot . Does anyone have an idea what it can be ?
*it has a tank mate that does not have anything on its skin.
* I did a complete water change and started using antibacterial liquid.
If you have any suggestions let me know .
Thank you !

 

[Tom]

Its likely a bite from the other one. They shouldn't be kept in pairs. Groups can work, but not pairs.

Is there any salt in the water? That will help them fight infection.

 

[Darklightning07]

There is not . Do you use the same salt water salt or anything different? Also how much salt .