What does buttermilk do to fried shrimp batter? I have been using ice water in my shrimp batter and it seems to make the batter too hard after frying them.  Would replacing the ice water with buttermilk make the batter less hard but still crispy?
Yes, the fat in the buttermilk should result in a slightly softer, less brittle, batter. The exact crispiness will depend on frying temperature and duration of course.