Criminal Ryukin in prision

made some amateur mistakes on my first tank with 3 Ryukin and a
common. They got sick so I got to learning fast and have brought them
back (mostly) from very poor condition. Problem is one of the Ryukin
(that didn't get very sick, is now very strong with the medicines, etc
& now harassing still weaker, healing fish (both common & Ryukin.
They're looking poor & now missing parts of fins.

So I put him in jail; a five gallon bucked with aged, dechlorinated,
aerated water and a little salt. (The same thing worked wonders
-overnight - for the common to get him to relax & heal from not
getting beaten up all the time). Is there any hope of having my bad
boy (strong swimmer, bright reds, with beautiful flowing fins) join
the group or should I expect that it will strike again even after they
are fully recovered & should keep him isolated. FWIW his fins were
nipped when I got him. I assumed he got a little fresh with someone
in the store tank. If it could grow back it'd be beautiful.

TIA