1 teaspoon epsom salt? Solid?
Flush. IF it is still sitting on the soil surface, pick it ALL out. That plant may not survive.
Dosage for epsom salt is 1/4teaspoon per gallon of water. I NEVER add it to soil. I use it as a foliar spray only when I see distinct signs of a Mg deficiency, and these days I just foliar feed with a complete micronute (GH Micro or Algoflash) to treat.

Yes, your pH was too high. But you need to adjust it by a correct flush. There's an instruction at the top of the problems section. Use the lemon juice or pH down to make a solution at pH 6-6.5 and pour it through until the water coming out the drain holes has a pH of 6.7.

I'd start some more seeds too.