You could just have a strain that likes more Magnesium. It’s actually pretty common with all the hybrid strains now. If you were depleted of Magnesium I would think that you’d also be showing signs of a calcium deficiency. The two commonly go hand in hand.
But if your in a 1gal pot, I’d definitely start planning a transplant to a larger container in the near future. Pre mixed soil only lasts about 1 -1.5 months before the plants need more nutrients.
So Epsom salts is just Magnesium Sulfate, it’s found local at grocery stores, Walgreens, Wal-Mart, Amazon, ect. It’s in the bath and beauty department, sold as a additive for uses such as soaking feet, or adding to the bath tub for sore muscles. It very cheap too, 4lbs for like $3.50
Just make sure that it’s not scented with shit like lavender. Just get the plain stuff.