You made some assumptions about NO3.
1.Light drives CO2 uptake and that can drive NO3 uptake, that's a safe assumption, reasonable etc.
2. The NO3 test kit was correct, this is not so reasonable.........if you calibrate it, then you'll know, making a solution of 1-5-10-2-ppm ought to tell how good it is....or is not.........
If the tank is fairly limited by just N alone, then a one day uptake of 8 ppm of NO3 may occur, but generally even at high light levels, 4ppm NO3/day is a lot.
Some denitrification may occur in older substrates, but that's not been addressed well by anyone in the hobby to date, I've threatened to, but it'll be awhile before that gets done.
Dose wise, you are on track, that sounds about right for the tap and the tank etc.
I'd suggest perhaps switching to Tropica master grow in place of the Fe/AE product. Otherwise from here, at least for the environmental ranges, you are in good shape.
CO2 is about all that's left to play with.
Regards,
Tom Barr