is this fin rot

If it is indeed flukes, you will have to treat ALL your fish. The problem with flukes is you usually can't see them unless they are on the eyes or fins. If one fish has it, most likely all the fish in the system have it.

Prazipro works well for flukes. The bottle says 2 treatments is enough. From experience I would suggest 3 treatments. I had 2 outbreaks of flukes in 2010 - 2011. The first outbreak occurred around June 2010 and I followed the directions and did 2 treatments. That helped but 6-8 months later it came back. I haven't added any new fish to my 300 FOWLR since late 2009 so I knew this was the same outbreak I treated in the past. So, the second time around I did 3 treatments and I've been fluke free for almost 18-20 months (keeping fingers crossed ).

Good Luck.