Sand works for up to 4 weeks or so IMO- but here is the info. off the cherrystone grit bag:
http://cherrystonegrit.com/grit_sizes.html
#1 is for up to 4 weeks or so
#2 is for 4-7 weeks (and I use it for bantams too)
#3 is for over 7 weeks
(this info is off the bag from the feed store of this...