Nutrients

If someone says mix different brands they do not have any idea what crap is comming out their mouth. It is chemistry, and some stuff doesn't play nice together

Do not mix. Can have chemical reactions that could kill your plant. Avoid as much as possible.

still need right ratio and concentration to match your environment in the end... whether soil, soilless or hydro... same components (once broken down) build the same parts of the plant.

it won't matter... have to worry about the same stuff as always.. i'd just make sure to mix whatever contains teh majority of your calcium after other components have been dissolved or mixed in first. Calcium can form precipitates more easily than other molecules invovled. If the things that provide S are dissolved, you don't have to worry about a temporarily high concentration as it dissolves or mixes in encountering high concentrations of caclium etc... for the most part, there's only a few optiosn to provide various nutrients needed... they are not all equal, but probably not much difference between them either. there's a pool of ubiquitout options and it's very unlikely you'll find a volatile combination realtive to what is used for fertilizer.