A calcium reactor uses c02 to dissolve a calcium carbonate media boosting your calcium levels and your alkalinity as well
AS far as feeding the reef goes that really depends on what you want to keep, i feed my softy and sps tank with a coral food recipie i took off the forum, basically just ground up seafood and various larval diets and fish foods
A calcium reactor is pretty essential for an sps tank, but softy and lps tanks aren't such a burden on your Ca levels so they aren't required
I borrowed this, I asked this same question the other day. Hope that helps. I can send you the link to this thread if you give me your email.
Leopard