Overapplication of magnesium sulfate will cause nutrient lockout.
Have you read the epsom salt sticky?

Epsom salts not a miracle cure...
Rusty Trichome Reviewed by Rusty Trichome on . Fan Leaves Dying! Got a problem with my northern lights, took them as cuttings, grew nice and well for 2 weeks, put them into bud they started to hair up nicely then they suddenly took a dive all the leaves started to show a mag def, so i gave em some epsom and made sure my temps were ok, they are 18.6lowest at night, and about 23 in the day, using biobizz according to their schedule, in a standard multi purpose compost from wilkos, currently under 250w hps with a 125mm exhaust fan and passive intake, after Rating: 5