Your conflicting reports are due to the fact that no one knows, with certainty, where to place an ideal recommendation. We all find our way to healthy tanks, but there is so much variability in our individual approaches that you get what seem to be contradicting reports. Some people have 50+ppm and report that dosing less causes problems, some recommend 10ppm and report that more causes problems.
Personally, I think itís a function of the relation to other nutrients (look up ďMulderís chartĒ). I was dosing EI levels (30-40ppm weekly) and had a healthy tank. Iíve reduced this to dosing 15ppm weekly and still have a healthy tank, but all my other nutrients have changed as well. I estimate that, with my current setup and dosing, my plants consume about 10ppm weekly.
I try to fit my macros into a scheme using ionic balancing, which forces me to roughly balance the dosing of N, P, K, Ca, Mg and S in relation to each other (traces play a small part, as well). Itís very similar to a forced-choice decision matrix and there is certainly a lot of slop in it, e.g.; fish contribute N and P that canít be easily measured, but it gives me a warm feeling.
So, like all the nutrients, it is probably a function of inter-relationships. Look at threads containing journals to see the various balances that you might like. You might also take a look at the PPS approach to nutrient balancing, if you want to be in the lower-dosing area vs. EI, which balances in the higher-dosing area.