I too have read that sand shouldn't be added to clay...after my FIL added sand to my daylily beds last year
. It may have some benefits, but I think there are other substances that could be added that would have more benefits and no potential deficits. My plan for now is to add a lot of compost and good black fill dirt (I can get a truck load fairly reasonable around here) and then add whatever nutrients it might be needed based on a soil test.