Nutrients

You use a combination (balance the overall levels) according to what you consider the plants need. More strictly, that'd be relative to the growth stage, the nutrient balance in each formulation, concentration and your setup and plant's status. Don't just pile on multiple bloom/flower/pk nutes at specified strength. Vaguely speaking, if you use 3 nutes, use 1/3rd concentration each (but then you'd probably want to probably bias towards certain ones, depending). But I figure you probably know that, just saying in case someone thinks you should just add shit together. Oh and of course, alternating the nutes is also related to that. Like if you have 3 of the same class of nutrients, you use one, then the other. It depends a bit on how "mixable" the nutes are, in a sense...but that requires a bit of experience and familiarity with those products.