I do own a copy of your guide. I'll be rereading soon.Velcro, that I dedicated my Reef Guide Part 1 to entirely ;-)
If you have both in non detectable ranges, then you have to supplement both, and make adjustments to the system to avoid maintaining zero nutrients. Unless you run a real Zeo system of course.
I cut my refugium photoperiod in half just now. Test 0ppb P and undetectable NO3 again. Dosing NO3 to 0.25ppm and PO4 to 0.03ppm.
I'll pick up some ascorbic acid today and also some dr tim's bacteria. I only have his line available locally. I think they carry everything BUT "one and only." Do you have a recommendation on which to use?