I backwash until it's clear and then rinse til clear. Both usually start out clear - then dirty - then clear again.

I inherited my pool 7 years ago and just changed the sand over the weekend for the second time this past weekend becasue I was backwashing all the time. Took a couple hours and $25 for 150 lbs. of sand. I add a little DE to my sand through the skimmer which greatly enhances filtering but does cause me to have to backwash a little more often. Well worth the price for crystal clear water!