Rescued Betta

#2
yes finrot for sure...and sometimes it can take a while to knock out diseases like that...especially if he was a 'rescue'. Most meds 'treatment time' needs to be doubled anyway...so 2weeks is not unheard of to have to treat for finrot. Watch for the blackness to fade, the fuzzy edges to go away, and for fin to start growing back. Once you start seeing fin regrowth, you can stop the JFC.

HTH :)