Hi I am new to all of this and have some questions. When you are all talking about dry ferts are they pure chemical or do they have filler? If I have a bottle of lab grad KN03 would that be the same as the dry ferts you are talking about? Also does anyone have a dosing regime in molar concentrations? Calculating ppm drives me nuts. I am particularly interested in a trace mix that has molar concentrations.
The dry chemicals we use are not lab grade chemicals, but agricultural grade. They are intended to be pure chemicals, with no intentional additives. I don't know why we use ppm concentrations vs. molar concentrations, but they aren't hard to do, until you add the complexity of expressing them in terms of a specific compound - like "carbonates as calcium carbonate".
As Hoppy mentioned, we use agricultural grade, but if you have access to lab grade, then all the better.
I use lab grade chemicals to make my 4 dkH reference solutions for my drop checkers.
As for ppm versus molar concentrations, it might be due to a combination of convention (whoever started it) and ease of expression; now, we can say x ppm of nitrates are required as opposed to y M(olar), etc.
The chemist in me understands your confusion though