I think once a week is perfectly fine. Especially since it takes that long to dry in moss. It's better to be a little dry then too wet i say! Most of my phals are in a coconut husk chip mix and I only water about once a week. Some of my smaller phals I may water every 5 days but only because they are in smaller pots and dry a little quicker. But that's just my personal experience, I'm definately not an expert!