I test my 55g reef every two weeks. I test for
PH, Aumonia, Nitrite, Nitrate, Silicates,Phostphates,
Alk and Calcium.
I only run a hang-on skimmer for my only mechanical filtration, so I like to keep a close eye on the water conditions in able to combat any minor fluctuations if they occur. Good news, I haven't detected any yet. My tank has been up for 1 year.
Howard