IMO, you definitely need to test for things like ph, calcium, alk, etc...regularly. Any reef tank needs to be chemically close to that of natural sea water. You need to maintain calcium, more than you can just do with small, regular water changes. You definitely don't need any reactors, but you should test for the above, and try to keep them stable. A simple two part calcium/alk additive, such as Kent CB, would do the job well. What do you test for?