I can't get NO3 to lower than about 8ppm on a very good day. I've never
added N directly to any of my tanks. On the other hand, PO4 seems to be
sucked away as if there's no tomorrow. I have to add PO4 every few days.
I'm not sure what's going on with K, but I do add K2O, haphazardly. I
need something to initially gauge what's going on with it so that I can
create a dosing regime.

Sounds like it could be nitrate leeching from your gravel. Two big water
chnages will get rid of most of that. I aim for 20-30ppm NO3 so I'd
still ad kno3 in your case.

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