I do not currently test for anything because my system has grown very predictable over the past year...there is little/no change in stocking on a monthly basis, so nutrient import and export is rather linear and so is the pH due to the calcium/alk dosing regimen. As far as I remember, I havent tested the pH, nitrate, calcium and alk in my reefs for maybe 8-10 months now.
It is interesting to note how a reef keeper can assess conditions in their particular system by looking at environmental cues, such as color and vigor of coralline deposition as well as the lateral growth of corals and other encrusting organisms. One simply must test in the early cycling stages to get a feel for the trends of a particular setup, but after its cruising we can back off all the adjustments provided stocking of the aquarium is fairly consistent.
Brandon M.