Thanks for the nice comment
To answer your first question...I make my own nutrient mix with the help of HydroBuddy
. This program makes all sort of calculations and returns me a list of Macro and Micro nutrients and their weight in grams needed to make a predefined amount of nutrient mix...
If you understand Dutch, I've made a basic usage tutorial here
I have all sorts of recipes in HydroBuddie's database. So I can make a nutrient mix for almost every crop you can imagine...
You probably have some experience with hydroponics...Because of your second question
Yes, singular nutrients (macro or micro) can get depleted. To measure one single substance one would need fairly expensive probes and that's beyond my hobby budget
You could measure the EC value of a mix, but that still wouldn't tell you which substance is getting low. I do measure the EC value (with a pen for the moment, but I'm working on a improved version of my controller), but this is to know how much concentration of nutrients are in my 200L tank...
To make sure I always have the right amount of singular nutrients in my tank (read: the recipe is still as it should be...) I do a nutrient change every 14 to 30 days. The waste goes to my conifers and grapevines...They also like the readily available nutrients