Mike
Once your tank is up and running, water quality doing well, NO3 is kind of moot. Is your macro growing well? Your nitrates are being taken care of. Is your macro suffering? Do you have algae all over? Maybe your P04 is high.
If every creature in the tank is doing well -- verts, inverts, etc. -- why bother with nitrate and phospate measurement? If the phosphate is zero on any scale you read, perhaps something in the tank is eathing it and keeping your biological filtration in balance. If it's high, you're going to have an "outbreak" of something -- who knows what -- and you'll then have to measure some level to see how to handle it.
Measuring a constant nitrate and phosphate level in a tank makes no sense. Be more concerned with Ca and dKH and Mg, and, of course, salinity. Those are the ones you need to keep balanced and copasetic.
I like bells and whistles, but it seems IMHO to make no sense to measure a constant NO3 or PO4, especially at a cost of $$ and constant calibration. Just my thoughts.
HAPPY TURKEY DAY EVERYONE!!