I also am pretty careful not to waste my time/money with tests that are not required, HOWEVER....if you have a tank with a lot of fast growing corals (and particularly if you have strong lighting) you DO need to test for alkalinity (I recommend once/week), calcium (once per month), and magnesium (once per two months unless you are doing lots of water changes). If you know how your tank 'runs' for these parameters you can test less often. These parameters can get out of balance over time. If you are using a balanced method of addition of calcium and alkalinity such as kalkwasser, calcium reactor, or two part supplement, then the imbalance will not occur quickly, but it can occur. FWIW, you can make your own alkalinity test kit reagent (we gave them out free at a club meeting a few months ago). For calcium I use the Hach test kit and dilute the sample to 1/7th normal conc., costs very little to use if you do it this way. I also use the Hach kit for Mg, but you might want to dilute your sample even more to save on reagent use.
