No. You can manually test and add calcium as needed. You will not know that until you get it setup. The more hard corals you have the more calcium will be consumed. Various other critters will consume CA as well. I believe a calcium reactor will give you a steady CA level.
like joe said a calcium reactor is just some thing that automaticlly adds calcium to your tank on a regular basis...until you have a tank full of hard corals it isnt nesacerry.... and even then its still just a convienance and not required
