We are not sure if it's fin rot, still. The aquarium salt will be fine if you have it on hand, but IAL is good for more than just treating fin rot.
Most of the time, if a fish has a minor tear like yours, it will heal back up in a matter of days with only clean, warm water, but the aquarium salt will help. Just keep an eye on his fins, as that could be his natural coloring and not fin rot. If you use AQ salt for 10 days and it has not disappeared, it probably is not fin rot. Avoid prolonged use of AQ salt.
If you can get your hands on IAL, prolonged use will not hurt him.