Ok Steve, I'm going to admit something. The only things I actively test for is Ca, Alk and Mg. it's a battle for me to keep Ca above 420, I struggle to keep Alk between 8-9 and Mg I try to keep above 1200.
As for po4, I run gfo through a reactor. I change it out about every 3 weeks or if I see red slime start growing on my sand. I handle No3 reduction just through water changes which I do about 15% every week. I tried bio pellets way back when I first got back in and didn't like it. I found that it was too hard to controll all the variables. I also run activated carbon through a reactor.
That's about it. I try to keep things as simple as possible.