Originally Posted by HD Blazingwolf
it is also possible that ur substrate is abosrbing it through cation exchange
I didn't consider that possibility. Good point.
I am now left with guessing an appropriate trace dose. Since the uptake of each nutrient is non linear. Any reason why too much trace would be detrimental? Maybe increasing it by 30% or so. I really don't trust iron tests anyway.
PS I have never heard a 6ppm/day uptake of NO3, guess I need to look around more.