It's hardly going to make a difference. Ag grade is usually 99%ish purity while pharma grade is 99.9%, lab grade being 99.99% or higher. The rest is water as it is.
Plants can handle a huge range of concentrations of every nutrient, so if you're adding magnesium sulfate as an additive to gain maybe an extra 20ppm of magnesium, that change in purity will give you an extra 0.1ppm. Hardly something to be concerned about.
Plants can handle a huge range of concentrations of every nutrient, so if you're adding magnesium sulfate as an additive to gain maybe an extra 20ppm of magnesium, that change in purity will give you an extra 0.1ppm. Hardly something to be concerned about.