Every tank I have done, I test all and complete parameters inside of normal FO mortality parameters. pH, Alk, Nit's, Ammonia.
For my reef, once my nitrogen cycle is complete, I just stick to using my pH meter, and keeping an eye on alkalinity, calcium and magnesium, but I typically dose according to my pH. I keep dosing per the tank demand as long as my pH is below 8.4. If my pH is at 8.3, I dose about half what i would normally, and at 8.2, I dose as normal.
There is nothing scientific about it, I've just noticed that the parameters tend to correlate within that spectrum as I want them to be, and I don't ever want to change my pH too dramatically between any period less than 24 hours. 1 tenth is never a problem, but anything more can be detrimental to everything's mortality.
I currently only test about once every two weeks for the Alkalinity, and the Calcium and magnesium only about once a month. I test my pH every time I dose; before and about 4 hours after. I also periodically test my salinity.