Please help! It's might be an easy fix or at least I hope it is

Hi there, if it's just one leaf, and it's got a rip, don't worry about it.. Unsure if the spraying of the magnesium sulphate could have caused it, but i wonder why did you spray her to start out with? Did she show any signs of deficiencies? Nutrients are usually salt, and if they dry out (i.e the water evaporates faster than the leaves can pick it up), this could leave a white residue. However in this case it's not easy to tell. You also said you sprayed the whole plant. If there are any water-droplets you know that together with the light, they can act like a magnifying glass in the sun and burn marks into the leaves, so usually it's best to only spray when the light has gone out. I would suggest to keep a good eye on her for the next few days and see if there's any change.