Mixing nutrients of different brands

what constitutes most fertilizers comes from a fairly limited set of options. They are ubiquitous.. you should think of various ingredients like generic Rx.. molecularly exaclty (though multiple mulecules provide n, p or k et al, and should be considered individually) the same, therefore same/similar effects. read teh detailed ingredients label and see it's the same stuff in slightly different options/combos. you have to worry about the same things that are always a concern. Primarly, what you are adding calcium to.. some things may need to be dissolved separately.. once dissolved it's generally not a concern unless you are making some stock, highly concentrated stuff. Calcium will easily form a precipitate with sulfur, i believe? if you just mean switching from one brand to next with the same plant, no big deal.. if the resulting concentration and ratio of nutrients is the same, you'll have similar results.