Nice fish, we'll done.You don't need a special tool, try Googling tube nail knot and such like, should turn something up.That said, to be worried about breakages, guessing you must have damaged the thin end of your leader. You can Just replace the damaged bit, doesn't need to be that technical, especially if your fishing wets. I would find where the leader is around 8 pound, cut it and tie on a length of 6 pound tippet.Good luck!