I used to use my pH probe as well as general appearance of my corals as guides to what was going on chemically in my tank. After reading the articles posted, I began testing and recording alk, Ca and Mg, rather sporadically at first.
Everything was way off at first, so I used the tank volume calculator, using inside the tank measurements, to figure out the exact water volume in each of our three tanks. Then I began dosing in small amounts like the reef chemistry calculator suggested, keeping track of what I was dosing and how much.
I've gotten into the habit of testing, recording test results and adusting levels bi-weekly. Each tank has different uptakes of alk, Ca and Mg and it varies from each testing period what has to be adjusted. So, now, I just keep at it knowing that the living organisms are using these chemistry components at different rates, even though we keep up with weekly water changes and other tank maintenance.
Corals are doing noticeably better now compared to how they looked before I began paying attention to water chemistry. And I thought they were doing okay without testing
