How often do you test?

[Reef Pilot]

I test alk and Ca every 2 or 3 days (unless I am away). N03 every month or so (always zero). P04 every 3 weeks or so, to see if my GFO needs changing or turning. Mg just before every water change to see if it needs topping up a bit. Salinity is tested before and after water changes. That's about it...