Don't use medication yet (unless the rotting has advanced greatly). Raise the temperature up to 80-82F (and if you're already at those temps, a couple degrees above that) and add salt. Catfish are sensitive to salt, though, so only add about a tablespoon for every five gallons of water.
Oh, before I forget. Fin rot is usually caused by poor water conditions, so I recommend you upgrade your filtration and/or tank (remember, both Arowanas and RTCs reach tremendous sizes, and so should have according homes).