Others will say different, but I usually wait til I have a 3/4 inch layer or so of lees falling out. If the layer doesn't form, I usually won't rack it. If I am going to sweeten it, I usually put the k-meta and sorbate in the bottom of a clean carboy and rack onto it. Then wait a week or two and sweeten, wait another week or two to make sure it doesn't referment and bottle. Just my way, Arne.