i'm not convinced most babies iron stores drop that significantly by six mos. this is from kellymom: "The original iron stores of a full-term healthy baby, combined with the better-absorbed iron in breastmilk, are usually enough
to keep baby's hemoglobin levels within the normal range
well into the second six months."
more here, check it out http://www.kellymom.com/nutrition/vitamins/iron.html