It's the type of nutes you use. If it's not immediately plant available, it contributes to elevated ppms. you have the ppms related to what 'feeds' the microbse, and the ppms of wffhat teh microbes spit out or otherwise break down that is plant avaialble. so you got inventory to feed the microbes and prodction from those microbes to feed the plant. the stuff that can't enter the plant can't cause a toxicity in the plant, obviously.
more is not always better. It's about teh right level of each nutrient element. Despite common belief, the plant doesn't all of a sudden require a 33% boost to p or k in mid to late flower. this is an urban myth disproven by more than one empirical study. If you underfed these things previously, then a boost might show a benefit, but that is a function of a previous underfeeding and not a 'boost'. the plant's metabolism isn't foie gras. can't just shove shit down it's throat and expect good things.
so, if you see toxicities result after using a 'booster' don't lie to yourself. too much was added if the plant shows toxicity issues. try a lower dose next time, etc.. take notes and keep refining your fertilization process until the plant grows well and does not show toxicity symptoms.