Hand temper Dark chocolate couverture by Callebaut 54.5% cocoa

I am using Callebaut Dark Chocolate for tempering by hand.It's my first attempt ,as mentioned on the package I heated and cooled and then reheated the chocolate.but next day there were white streaks on the tempered chocolate what could be the reason for that?What do I do to get perfect tempered chocolate by hand ?Thanx.Arti.
updated by @arti-jain: 04/13/15 12:18:22AM

did you mix it while doing so?
you did that just in a bowl or you have a marble for tempering?

my best gues is that you did not mix it.

What did you do with the tempered chocolate? Enrobe something, or just leave in the bowl? If it was all left in the bowl, you would get streaking from the large mass of chocolate and the latent heat of crystallization. If the streaking is on an enrobed piece, the chocolate wasn't truly in temper, or the room was too warm.