I"d leave the Krausen where it is. The less you mess with your beer the better, though it is pretty hard to kill... I went through a stage of mixing the Krausen back in after the first 48hrs of vigorous fermentation, the theory being it was full of yeasty/malty goodness. These days I just leave it until fermentation has finished, as mentioned, usually at least 14 days. The important factor being every time you open the lid you are releasing that protective co2 covering....