I am not certain if Scolley has jumped over to the Neptune controler yet, but once he did warn me about one thing on X10. You have to be able to disable something called "local control", by sniping a circuit lead or such. There is a diagram available on the web to show the procedure. Otherwise, sometimes the units will come on when you don't want them to, perhaps by a power spike or such. Also, there are a few other nuances he mentioned. If using for critical things like heat, CO2, or in my case, an auto water change, well, I could have a wet floor without some kind of fail safe backup to prevent some un wanted turning on.
Also, I was informed that they work much more reliably if all the modules are plugged into the same circuit. Unfortunately, do to a remodel in my ex garage, now fishroom, I have three different circuits running four different tanks, so X10 didn't seem as good of option for me. But I still want to try it out sometime. Pretty cool program, if you can get over the cheesy website and marketing of activehome.
Where did you read/hear about an incompatibility between PO4 & NO3? It's very ill-advised, and well known to be so, to mix traces (with iron) and PO4 due to the iron & phosphorus reaction, but PO4 & NO3? I know there was a post talking about that somewhere in the DIY section, but that's the only thing I've seen. It seems sometimes there's also confusion about what you're not supposed to mix PO4 with.
I believe the thread was by Wasserpest on his autodoser with a Aquarium Systems 606 pump. If I remember correctly, by mixing PO4 with the other Macros, one got a stinky foul dosing mixture much more quickly. After reading that, I never tried and still dose that manually. PO4 is the easiest one to dose with a syringe, anyhow.