Cal (Ying) - test and adjust once a month
Alk (and Yang) - test and adjust once a week or more, depends on how my corals look and feeding habits, I find this the most important part of my reef
Mag - test and adjust once a month, add once a month
Sal - test and adjust once a month, I have a ATO
Nitrate - don't test anymore
Ph - don't test anymore